(this as Writable<this>).field = ... no longer works in 5.9.0 #1515

Bug description

In 5.8.0, (this as Writable<this>).field = 4; would typecheck as expected with no errors, but in 5.9.0 it generates an error. <typeof this> also doesn't work.

class SomeClass {
	readonly field: number = 3;

	method() {
		(this as Writable<this>).field = 4; // worked in 5.8.0, error in 5.9.0
	}
}

Repro

https://www.typescriptlang.org/play/?#code/JYWwDg9gTgLgBDAnmApnA3gdSsGBDAIwBsUBfOAMyghDgHIlUBaClAZxjoG4BYAKH4BjInjZs4AZRooAwiLEZ+ASCgo8AEwgA7IokrAURdQC44WgK4gCKKHAC8cAMy8BfJSBQwAFhHUAKAEpFNyVvYDYAOgoDIxclJQB6BLgUuAA9AH5lUK9wqJj1ezgAFi44JLgUAA9UQRgUQptqKGyK1MzsvzDxUThsXEISAB5ugD4A-MNCh1Ly5IB3aABrBrhgLTgAVgiADgiABgAaSqhmtY3tgE4D1uTU+4fHh46Qrtye8X78YhQR5BQIBQEO9xpMjEVZhU8EQ2BA4Jp2FoGHBFlAlrcnpisU8XkpSPx8a5BNoOOcOHgtII0A4tCh5pJpHJRGxAi51uTKSgweoXG1Hi92fhOdyIWUKtVavVGqdoPw+c8snw-IKKVS4L0voNfowAUCVZzQdEpqK5ijlh9KjUUHUGnK7tiHY77i9lVoOWqNThvsMpB4mWJDQUTVCYXDUUsLRLrVK7U64-zFUA