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`.

library/modules/platform/android.sx

@@ -50,7 +50,7 @@ SurfaceHolder :: #foreign #jni_class("android/view/SurfaceHolder") {
     addCallback :: (self: *Self, cb: *SurfaceHolderCallback);
 }
 SurfaceView :: #foreign #jni_class("android/view/SurfaceView") {
-    static new :: (ctx: *JContext) -> *Self;
+    new        :: (ctx: *JContext) -> *Self;  // no `self: *Self` → class method
     getHolder  :: (self: *Self) -> *SurfaceHolder;
 }
 SurfaceHolderCallback :: #foreign #jni_class("android/view/SurfaceHolder$Callback") { }