ffi 3.2 C5: migrate uikit.sx view tree + GL drawables cluster

Final Phase 3.2 cluster. CALayer / CAEAGLLayer / EAGLContext declared
as `#foreign #objc_class` blocks, plus `setContentScaleFactor` added
to UIView and `-layer` now returns `*CALayer` (was opaque `*void`).

Classes declared:

- CALayer      → setOpaque (instance)
- CAEAGLLayer  → setDrawableProperties (instance)
- EAGLContext  → alloc (class), initWithAPI (instance),
                 setCurrentContext (class — takes EAGLContext arg),
                 renderbufferStorage_fromDrawable (instance),
                 presentRenderbuffer (instance)
- UIView       → +setContentScaleFactor (existing decl extended)

The C5 group sits above UIView in the file so the `-layer` return type
`*CALayer` forward-resolves cleanly.

Migration sites in uikit.sx:

- `uikit_create_gl_context` → `EAGLContext.alloc().initWithAPI(api)`
  + `EAGLContext.setCurrentContext(ctx)`.
- `uikit_setup_renderbuffer` → cast `*EAGLContext` and
  `gl_ctx.renderbufferStorage_fromDrawable(target, layer)`.
- `uikit_present_renderbuffer` → same cast + `presentRenderbuffer(target)`.
- Scene-connect bring-up: `gl_layer.setOpaque(1)`,
  `eagl_layer.setDrawableProperties(...)`,
  `gl_view.setContentScaleFactor(scale)`.

One more `objc_getClass(...)` lookup (EAGLContext) retired — the class
slot comes from the declarative binding via `__sx_objc_class_init`.

**Phase 3.2 complete.** Five clusters migrated (C1: Foundation
utility; C2: Notifications + Bundle; C3: RunLoop + display timing;
C4: UIKit chrome; C5: view tree + GL drawables). 8 foreign Cocoa
classes declared; ~30 `#objc_call(T)(...)` sites rewritten to
`recv.method(args)` / `Cls.method(args)`; 6 `objc_getClass`
lookups retired. Sx-defined classes (SxAppDelegate, SxSceneDelegate,
SxGLView, SxMetalView) and a handful of foreign sites that exercise
delegate/protocol surfaces stay on the explicit `#objc_call` form
pending Phase 3.7's class synthesis.

167/167 example tests; chess clean on macOS / iOS sim / Android via
`tools/verify-step.sh`.

library/modules/platform/uikit.sx

@@ -113,6 +113,25 @@ CADisplayLink :: #foreign #objc_class("CADisplayLink") {
     duration :: (self: *Self) -> f64;
 }
 
+// ── View tree + GL drawables (Phase 3.2 C5) ────────────────────────────
+// (Declared before UIView so `layer :: (...) -> *CALayer` can reference it.)
+
+CALayer :: #foreign #objc_class("CALayer") {
+    setOpaque :: (self: *Self, opaque: s8);
+}
+
+CAEAGLLayer :: #foreign #objc_class("CAEAGLLayer") {
+    setDrawableProperties :: (self: *Self, props: *void);
+}
+
+EAGLContext :: #foreign #objc_class("EAGLContext") {
+    alloc                            :: () -> *EAGLContext;
+    initWithAPI                      :: (self: *Self, api: s32) -> *EAGLContext;
+    setCurrentContext                :: (ctx: *EAGLContext);
+    renderbufferStorage_fromDrawable :: (self: *Self, target: u32, drawable: *void) -> s8;
+    presentRenderbuffer              :: (self: *Self, target: u32) -> s8;
+}
+
 // ── UIKit chrome (Phase 3.2 C4) ────────────────────────────────────────
 
 UIScreen :: #foreign #objc_class("UIScreen") {
@@ -122,11 +141,10 @@ UIScreen :: #foreign #objc_class("UIScreen") {
 }
 
 UIView :: #foreign #objc_class("UIView") {
-    safeAreaInsets :: (self: *Self) -> UIEdgeInsets;
-    addSubview     :: (self: *Self, view: *void);
-    // `-layer` returns a CALayer*; declared as opaque pointer for now
-    // (CALayer's own declarative binding is in the C5 cluster).
-    layer          :: (self: *Self) -> *void;
+    safeAreaInsets        :: (self: *Self) -> UIEdgeInsets;
+    addSubview            :: (self: *Self, view: *void);
+    layer                 :: (self: *Self) -> *CALayer;
+    setContentScaleFactor :: (self: *Self, scale: f64);
 }
 
 UIWindow :: #foreign #objc_class("UIWindow") {
@@ -526,17 +544,14 @@ uikit_keyboard_will_change_frame :: (self: *void, _cmd: *void, notification: *vo
 uikit_create_gl_context :: (plat: *UIKitPlatform) {
     inline if OS != .ios { return; }
 
-    EAGLContext := objc_getClass("EAGLContext".ptr);
-    // UIScreen class slot comes from the declarative #objc_class binding.
-
     // Read the screen scale up-front so callers can size font caches and
     // textures with the right DPI before the window even exists.
     screen := UIScreen.mainScreen();
     plat.dpi_scale = xx screen.nativeScale();
 
-    ctx_raw := #objc_call(*void)(EAGLContext, "alloc");
-    plat.gl_ctx = #objc_call(*void)(ctx_raw, "initWithAPI:", EAGL_API_GLES3);
-    #objc_call(void)(EAGLContext, "setCurrentContext:", plat.gl_ctx);
+    ctx := EAGLContext.alloc().initWithAPI(EAGL_API_GLES3);
+    plat.gl_ctx = xx ctx;
+    EAGLContext.setCurrentContext(ctx);
 
     load_gl(@ios_gl_proc);
 }
@@ -611,12 +626,13 @@ uikit_scene_will_connect_ios :: (delegate: *void, scene: *void) {
     win.setRootViewController(plat.root_vc);
 
     gl_view : *UIView = xx plat.gl_view;
-    plat.gl_layer = gl_view.layer();
+    gl_layer := gl_view.layer();
+    plat.gl_layer = xx gl_layer;
 
     // Mark the layer opaque (no compositor blend). Required for EAGL +
     // recommended for Metal (CAMetalLayer.opaque defaults to YES but doesn't
     // hurt to be explicit).
-    #objc_call(void)(plat.gl_layer, "setOpaque:", xx 1);
+    gl_layer.setOpaque(1);
 
     if plat.gpu_mode == .gles {
         // EAGL drawable properties dict required by
@@ -634,7 +650,8 @@ uikit_scene_will_connect_ios :: (delegate: *void, scene: *void) {
         dict := NSMutableDictionary.dictionary();
         dict.setObject_forKey(xx ns_no, retained_key);
         dict.setObject_forKey(rgba8_value, colorformat_key);
-        #objc_call(void)(plat.gl_layer, "setDrawableProperties:", xx dict);
+        eagl_layer : *CAEAGLLayer = xx gl_layer;
+        eagl_layer.setDrawableProperties(xx dict);
     }
 
     // EAGLContext + load_gl were already done in uikit_create_gl_context()
@@ -647,7 +664,7 @@ uikit_scene_will_connect_ios :: (delegate: *void, scene: *void) {
     screen2 := win.screen();
     scale := screen2.nativeScale();
     plat.dpi_scale = xx scale;
-    #objc_call(void)(plat.gl_view, "setContentScaleFactor:", scale);
+    gl_view.setContentScaleFactor(scale);
 
     // Renderbuffer is allocated lazily in -[SxGLView layoutSubviews] once
     // the layer has its real on-screen bounds. makeKeyAndVisible triggers
@@ -691,7 +708,8 @@ uikit_setup_renderbuffer :: (plat: *UIKitPlatform) {
 
     glBindRenderbuffer(GL_RENDERBUFFER, plat.color_renderbuffer);
 
-    #objc_call(bool)(plat.gl_ctx, "renderbufferStorage:fromDrawable:", GL_RENDERBUFFER, plat.gl_layer);
+    gl_ctx : *EAGLContext = xx plat.gl_ctx;
+    gl_ctx.renderbufferStorage_fromDrawable(GL_RENDERBUFFER, plat.gl_layer);
 
     glBindFramebuffer(GL_FRAMEBUFFER, plat.framebuffer);
     glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, plat.color_renderbuffer);
@@ -723,7 +741,8 @@ uikit_setup_renderbuffer :: (plat: *UIKitPlatform) {
 uikit_present_renderbuffer :: (self: *UIKitPlatform) {
     inline if OS != .ios { return; }
     glBindRenderbuffer(GL_RENDERBUFFER, self.color_renderbuffer);
-    #objc_call(bool)(self.gl_ctx, "presentRenderbuffer:", GL_RENDERBUFFER);
+    gl_ctx : *EAGLContext = xx self.gl_ctx;
+    gl_ctx.presentRenderbuffer(GL_RENDERBUFFER);
 }
 
 // ── SxGLView class ─────────────────────────────────────────────────────────