ffi: drop static keyword on foreign-class methods; param type discriminates

`static name :: ...` was redundant — instance methods always declare
`self: *Self` as their first param by convention. The parser now derives
`is_static` from the first param's TYPE: if it's `*Self` the method is
an instance method; anything else (including no params at all) is a
class method. Removes a token from the surface, keeps the dispatch
behavior identical.

The receiver param's NAME doesn't matter — only its type. Calling the
first param `this`, `me`, `receiver`, etc. is fine as long as the type
is `*Self`. This mirrors how the rest of sx handles receiver dispatch.

Migration of every site that used the keyword:

- `library/modules/platform/android.sx` — `SurfaceView.new(ctx)`.
- `examples/ffi-jni-class-03-static.sx` — `Math.abs(n)`.
- `examples/ffi-jni-main-03-ctor.sx` — `SurfaceView.new(ctx)` in the
  `#jni_main` body.
- `examples/ffi-objc-dsl-05-static.sx` — NSObject's `.class()` /
  `.description()`.

164/164 example tests; chess clean on macOS / iOS sim / Android via
`tools/verify-step.sh`.

examples/ffi-jni-class-03-static.sx

@@ -1,16 +1,16 @@
-// Phase 2 step 2.3 (PLAN-FFI.md): xfail then green for the `static`
-// method body item inside a `#jni_class` declaration.
+// Phase 2 step 2.3 (PLAN-FFI.md): xfail then green for class/static
+// method declarations inside a `#jni_class` body.
 //
-// `static name :: (args...) -> Ret;` declares a class/static method —
-// no implicit `self`, dispatched via `GetStaticMethodID` / `CallStatic*`
-// at lowering time (Phase 2.12). Step 2.3 extends `parseJniClassDecl`
-// to recognise the `static` prefix and mark the resulting
-// `JniMethodDecl` with `is_static = true`.
+// Instance vs class method is determined by the first param's TYPE:
+// `(self: *Self, ...)` ⇒ instance, anything else (here, `(n: s32)`)
+// ⇒ class method, dispatched via `GetStaticMethodID` /
+// `CallStatic*` at lowering time (Phase 2.12). No explicit `static`
+// keyword; the param shape carries the signal.
 
 #import "modules/std.sx";
 
 Math :: #foreign #jni_class("java/lang/Math") {
-    static abs :: (n: s32) -> s32;
+    abs :: (n: s32) -> s32;  // no `self: *Self` → class method
 }
 
 main :: () -> s32 {

examples/ffi-jni-main-03-ctor.sx

@@ -13,7 +13,7 @@ Bundle  :: #foreign #jni_class("android/os/Bundle") { }
 JContext :: #foreign #jni_class("android/content/Context") { }
 
 SurfaceView :: #foreign #jni_class("android/view/SurfaceView") {
-    static new :: (ctx: *JContext) -> *Self;
+    new :: (ctx: *JContext) -> *Self;  // no `self: *Self` → class method
 }
 
 g_held_view : *void = null;

examples/ffi-objc-dsl-05-static.sx

@@ -17,11 +17,12 @@
 
 NSObject :: #foreign #objc_class("NSObject") {
     // `+(Class)class` — niladic, name verbatim, selector = "class".
-    // Returns the class object itself.
-    static class :: () -> *void;
+    // Returns the class object itself. No `self: *Self` first param ⇒
+    // class method (sx parser keys on the param TYPE).
+    class :: () -> *void;
     // `+(NSString *)description` on the class returns a description
     // string. Niladic, selector = "description".
-    static description :: () -> *void;
+    description :: () -> *void;
 }
 
 main :: () -> s32 {