Fix async arrow this capture in static field emit

[Copilot]

Downleveled async arrows in static field initializers captured ambient this instead of the class constructor. This produced incorrect __awaiter(this, ...) emit when the initializer was moved outside the class body.

• Emit behavior

  • Mark async arrows inside static field/static block initializers with the class constructor capture.
  • Use that captured class reference as the __awaiter thisArg.

• Regression coverage

  • Added a compiler test for a namespace-wrapped static async arrow initializer.
  • Updated related async-arrow-in-class baselines.

namespace NS {
  export class C {
    static h = async () => 1;
  }
}

Now downlevels to:

var _a;
class C {
}
_a = C;
C.h = () => __awaiter(_a, void 0, void 0, function* () { return 1; });