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`.

current/CHECKPOINT-FFI.md

@@ -600,27 +600,46 @@ matching the expected output.
 
 Phase 3.2 C4 landed: UIKit chrome cluster migrated. Six classes
 declared (UIScreen, UIView, UIWindow, UIViewController, UITextField
-— plus the existing C1/C2/C3 classes already in place). Migration
-sites: `show_keyboard` / `hide_keyboard` use `tf.becomeFirstResponder()`
-/ `tf.resignFirstResponder()`; `uikit_refresh_safe_insets` uses
-`gl_view.safeAreaInsets()`; `uikit_read_screen_scale` and the GL-
-context bring-up both use `UIScreen.mainScreen().nativeScale()`;
-keyboard-frame callback uses `win.screen().bounds()`; the scene-
-connect bring-up chains `UIWindow.alloc().initWithWindowScene(scene)`
-and `UIViewController.alloc().init()` then `vc.setView(...)`,
-`win.setRootViewController(...)`, `gl_view.layer()`,
-`UITextField.alloc().init()`, `gl_view.addSubview(...)`,
-`win.makeKeyAndVisible()`. Three `objc_getClass(...)` calls (UIWindow,
-UIViewController, UITextField) are gone — the class slots come from
-the declarative bindings via `__sx_objc_class_init`. C4 is the
-cluster that triggered issue-0043; with the fix in, the chained
-dispatch resolves correctly under lazy lowering. 167/167 tests +
-chess clean on macOS / iOS sim / Android.
+— plus the existing C1/C2/C3 classes already in place). Three
+`objc_getClass(...)` calls (UIWindow, UIViewController, UITextField)
+are gone — the class slots come from the declarative bindings via
+`__sx_objc_class_init`. C4 is the cluster that triggered
+issue-0043; with the fix in, the chained dispatch resolves
+correctly under lazy lowering.
+
+Phase 3.2 C5 landed: view tree + GL drawables cluster migrated.
+CALayer (`setOpaque`), CAEAGLLayer (`setDrawableProperties`), and
+EAGLContext (`alloc`, `initWithAPI`, `setCurrentContext`,
+`renderbufferStorage_fromDrawable`, `presentRenderbuffer`) declared.
+UIView gained `setContentScaleFactor` and `layer` now returns
+`*CALayer` (was opaque `*void`). Migration sites:
+`uikit_create_gl_context` uses `EAGLContext.alloc().initWithAPI(...)`
+then `EAGLContext.setCurrentContext(ctx)`;
+`uikit_setup_renderbuffer` uses
+`gl_ctx.renderbufferStorage_fromDrawable(...)`;
+`uikit_present_renderbuffer` uses `gl_ctx.presentRenderbuffer(...)`;
+the scene-connect bring-up uses `gl_layer.setOpaque(1)`,
+`eagl_layer.setDrawableProperties(...)`, and
+`gl_view.setContentScaleFactor(scale)`. One more `objc_getClass`
+(EAGLContext) gone. 167/167 + chess clean on macOS / iOS sim /
+Android.
+
+**Phase 3.2 complete.** Surface summary:
+
+- `#selector("explicit:")` override (parts A1+A2).
+- Locked-in golden mangling-table test (part B).
+- Five uikit.sx clusters migrated to declarative `#objc_class`
+  (parts C1..C5) — 8 foreign Cocoa classes declared, 30+
+  `#objc_call` call sites rewritten to `recv.method(args)` /
+  `Cls.method(args)` form. 6 redundant `objc_getClass(...)` lookups
+  retired. Sx-defined classes (SxAppDelegate, SxSceneDelegate,
+  SxGLView, SxMetalView) and a handful of foreign sites that
+  exercise less common paths (e.g. `objc_call(void)(delegate,
+  "setWindow:", ...)` from UIWindowSceneDelegate protocol) stay on
+  the explicit `#objc_call` form pending Phase 3.7's class-synthesis
+  work.
 
 Open work:
-- **Phase 3 step 3.2 — C5** — uikit.sx migration (view tree + GL
-  drawables: CAEAGLLayer, EAGLContext, plus any remaining
-  CAMetalLayer / NSTimer sites).
 - **Phase 3 step 3.3** — `property name: Type` synthesizes
   `inst.name` → `[inst name]` getter and `inst.name = x` →
   `[inst setName: x]` setter. `#setter("...")` overrides the setter