feat: Allow mixin constructors with type arguments

[bb010g]

This constraint can be loosened without breakage.

Partially fixes #24122.

Example code that now works:

type Constructor<T> = new(...args: any[]) => T;

class A {
    a!: number;
}
class B {
    b!: number;
}
function mixinC<TBase extends Constructor<{}>>(Base: TBase) {
    return class C<T> extends Base {
        c!: T;
    };
}

const ACB = mixinC(A)<B>;
const acb = new ACB();
const acbC: B = acb.c;

Previously, compiling the class expression would fail with error TS2545:

tests/cases/compiler/mixinGeneric.ts:10:18 - error TS2545: A mixin class must have a constructor with a single rest parameter of type 'any[]'.

10     return class C<T> extends Base {
                    ~

It errors because unapplied C's constructor has a type signature of new <T>(...args: any[]) => C<T>. However, this doesn't turn out to be an issue. Code & types generate properly, and applying the resulting generic type properly monomorphizes new (e.g. ACB: new (...args: any[]) => mixinC<typeof A>.C<B>).

[typescript-bot]

The TypeScript team hasn't accepted the linked issue #24122. If you can get it accepted, this PR will have a better chance of being reviewed.

[sandersn]

To help with PR housekeeping, I'm going to close this PR while it's still waiting on its bug to be accepted. Once the bug is accepted, we can move on to reviewing the code change. In the meantime it goes stale too easily to be useful.