The UIKitPlatform struct had a string of '*void = null; // UIWindow*'
fields — the type lived in a comment, every callsite had to 'xx'-cast
back to the real type. Migrated to the real foreign-class pointer
types now that M3 declared all the relevant '#objc_class' aliases:
window: ?*UIWindow
root_vc: ?*UIViewController
gl_view: ?*UIView (SxGLView OR SxMetalView — both extend UIView)
gl_layer: ?*CALayer (CAEAGLLayer OR CAMetalLayer)
gl_ctx: ?*EAGLContext
display_link: ?*CADisplayLink
Each field is wrapped in '?' since the platform may not have set
it yet (gl_ctx is null in metal mode, display_link is null before
the first frame, etc.).
SxSceneDelegate's window getter/setter now take/return '?*UIWindow'
instead of '*void' so calling code doesn't need an xx-cast.
Required fix in objcTypeEncodingFromSignature: '?T' (optional) was
bailing with 'type kind not yet supported'. Apple's runtime treats
nullability as 'pointer may be null' — the wire encoding is the
same as T. Recursive unwrap handles ?*UIView → '@', ?*CADisplayLink
→ '@', etc.
Chess on iOS-sim: board renders, full pipeline intact. 183 tests
+ zig build test green.
f75923af00