ffi 1.26: uikit_chdir_to_bundle via #objc_call

Second Phase 1D cluster. NSBundle.mainBundle.resourcePath chain now
dispatches through `#objc_call(*void)` instead of a shared `msg_o`
typed cast — covers both class-method (`+mainBundle`) and
instance-method (`-resourcePath`) shapes through one intrinsic. Net
-3 lines.

iOS-sim chess regression smoke: app launches with all piece assets
rendered, which is the visible signal that `chdir` to the bundle's
resource path still succeeds.

library/modules/platform/uikit.sx

@@ -276,11 +276,8 @@ uikit_refresh_safe_insets :: (plat: *UIKitPlatform) {
 uikit_chdir_to_bundle :: () {
     inline if OS != .ios { return; }
     NSBundle := objc_getClass("NSBundle".ptr);
-    sel_main_bundle   := sel_registerName("mainBundle".ptr);
-    sel_resource_path := sel_registerName("resourcePath".ptr);
-    msg_o : (*void, *void) -> *void = xx objc_msgSend;
-    bundle := msg_o(NSBundle, sel_main_bundle);
-    rsrc := msg_o(bundle, sel_resource_path);
+    bundle := #objc_call(*void)(NSBundle, "mainBundle");
+    rsrc := #objc_call(*void)(bundle, "resourcePath");
     if rsrc == null { return; }
     chdir(c_string(rsrc));
 }