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-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 {