Add RegExp indices

[xiBread]

Fixes #44227

[typescript-bot]

The TypeScript team hasn't accepted the linked issue #44227. If you can get it accepted, this PR will have a better chance of being reviewed.

[rbuckton]

I'm not sure if we should be more pedantic here or not. [number, number] | undefined is a more accurate type, since a failed capture in an alternative can produce undefined:

const match = /(a)|(b)/d.exec("b")
match.indices[1]; // undefined
match.indices[2]; // [0, 1]

However, we use string instead of string | undefined in RegExpExecArray, so maybe this is fine.

[ImUrX]

any news?

[pagoru]

Come on...

[rbuckton]

Superseded by #52085