ffi 2.3 green: static body items in #jni_class

`JniMethodDecl` gains `is_static: bool = false`. parseJniClassDecl's
body loop now recognises a `static` identifier prefix (context-sensitive
— `static` stays a plain identifier elsewhere) and consumes it before
the method name, setting `is_static` on the resulting decl. Dispatch
to `GetStaticMethodID` / `CallStatic*Method` arrives in Phase 2.12.

122/122 examples green.

src/ast.zig

@@ -538,6 +538,7 @@ pub const JniMethodDecl = struct {
     params: []const *Node, // type_expr nodes — first is `*Self` for instance methods
     param_names: []const []const u8,
     return_type: ?*Node, // null = void
+    is_static: bool = false, // true for `static name :: ...`
 };
 
 pub const JniClassDecl = struct {