Review ts-internal

[aciccarello]

TypeDoc uses functions which the TypeScript team considers internal and exposes the types in ts-internal.ts.

We should review these methods to see if:

1. The methods are still considered private (marked @internal) by the TypeScript team
2. There is an alternative method (hopefully public) that should be used instead
3. We could engage the TypeScript team about exposing an api publicly so we are less likely to have breaking changes

[aciccarello]

There are some relevant comments on @christopherthielen's #310 and #314 PRs

[Gerrit0]

0.20 does a pretty good job of cleaning this up. There are only two things left in it, one of them has an issue that I expect will be accepted to be made public. The other... is deeply integrated into how typedoc works, isn't going to be exposed by the TS team, and will just have to be lived with for a while.

typedoc/src/lib/ts-internal.ts

Lines 1 to 19 in 33c2bc6

	import * as ts from "typescript";
	/**
	* Expose the internal TypeScript APIs that are used by TypeDoc
	*/
	declare module "typescript" {
	interface Node {
	// https://github.com/microsoft/TypeScript/blob/v4.1.3/src/compiler/types.ts#L847
	symbol?: ts.Symbol;
	}
	interface TypeChecker {
	// https://github.com/microsoft/TypeScript/blob/v4.1.3/src/compiler/types.ts#L4145
	// https://github.com/microsoft/TypeScript/issues/42118
	getTypePredicateOfSignature(
	signature: ts.Signature
	): ts.TypePredicate | undefined;
	}
	}