Provide a `this` type for `get`/`set` methods in `Reflect.defineProperty` options

Code

var A: {a?: number, b: number} = {b:2}
Reflect.defineProperty(A, 'a', {
  // set(this: any, value: any) { // to fix
  set(value: any) {
    console.log(this.b); // Property 'b' does not exist on type 'PropertyDescriptor'.
  },
  enumerable: true,
  configurable: true
});
A.a = 1;
// expect the context of setter is A

Expected behavior:

expect the context of the setter is A

Actual behavior:

Property 'b' does not exist on type 'PropertyDescriptor'.

Playground Link:

https://www.typescriptlang.org/play/index.html?strictPropertyInitialization=false&alwaysStrict=false&experimentalDecorators=true&emitDecoratorMetadata=true#code/LAKAbghgTgBAggLhgbwgfiQOwK4FsBGAplADQz5Z5FQC+MAvChQEw2gBKhAZgDaEDGAFwB0AE24BLTIQAKUAPYAHYoICeACjhkA5BG1lkoGDADOhQesg9shJBEyqAlCiPGY-eZhPy+wnvIBzdUEACwkTYXxHAG4YAHo4mDklFVUYbXxtGFF5QhMYTHlBGEIAD3Dizxg1ZXTk5Sg1ABE8-igJRUF5KG1hVxoSV0IcXGIIfD4kQSgbQZBjD0wuCQDsKHHJ6pnCUBoY0DhhCAYYAEZo0ASS0uUhapDCd09BMsquU3MX2HD4IA

Start with the linked TypeScript Playground example and compare the setter's inferred this with the expected receiver type. Trace the Reflect.defineProperty options and PropertyDescriptor typings, then add coverage for the example in an appropriate existing test area. Done means the setter context is typed as the target object without the reported error.