Revert "ES2020: fix String.prototype.matchAll type and description"

[jakebailey]

Reverts #62873

It did not fix the linked issue, but instead actually "fixed" #47310, which is marked as working-as-intended for the same reason as why we ban other params for strictness' sake.

[Copilot]

Pull request overview

This PR reverts a previous change that modified the String.prototype.matchAll type signature. The revert restores the original behavior where matchAll only accepts RegExp parameter instead of RegExp | string, aligning with TypeScript's strictness policy on similar methods.

• Reverts the type signature of String.prototype.matchAll from accepting RegExp | string back to only RegExp
• Updates JSDoc description to reflect the reverted parameter type
• Updates test baseline to match the reverted type signature

Reviewed changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated no comments.

File	Description
src/lib/es2020.string.d.ts	Reverts matchAll parameter type from RegExp | string to RegExp and updates JSDoc
tests/baselines/reference/stringMatchAll.types	Updates type baseline to reflect reverted matchAll signature

[jakebailey]

for posterity for other readers, see thread at #62873 (comment)