support TS 4.3 override syntax in class

[g-plane]

Reference: https://devblogs.microsoft.com/typescript/announcing-typescript-4-3-beta/#override-and-the-noimplicitoverride-flag

[Skalman]

@g-plane, just wanted to double check one thing. I saw a commit message "disallow override to precede accessibilities". Not really sure what you mean, but does the following still work as expected?

class B {}

class C extends B {
    override private constructor() {
        super();
    }
}

TS playground

[g-plane]

@Skalman I did it based on this: https://github.com/microsoft/TypeScript/blob/2f0c8b2bea3554f9371e1d2076df49498d12c5a7/tests/baselines/reference/override5.errors.txt#L5 .

[g-plane]

Let's see how TypeScript team answers: microsoft/TypeScript#43533 . If I'm wrong, I'll update this PR.

[g-plane]

As this PR of TypeScript: microsoft/TypeScript#43544 , accessibility modifiers must precede override, so there's no need to change in this PR, but maybe I need to add another check: microsoft/TypeScript#43533 (comment) .

[g-plane]

microsoft/TypeScript#43533 is closed because microsoft/TypeScript#43544 is merged, so we can go ahead.

[kdy1]

LGTM. Thank you a lot!