refactor: enable noUncheckedIndexedAccess

[sapphi-red]

Description

Enabled noUncheckedIndexedAccess to reduce errors for #18798

This would make the code safer but it's tedious in some cases like for (const key in obj) { obj[key] }.

[bluwy]

On surface I like that it encourages safer code, but it feels like it's making the code a bit more verbose in some cases. For example, it not interpreting regex access well and the const..in patterns affects the code readability for me. So I'm a bit conflicted in this change, but happy to hear what others think about this.

[sapphi-red]

Pushed a commit that adds String::split / String::matchAll / RegExp::exec overload. This should reduce the verbosity a lot. We still need to pass the type argument but it's easier than as StrictRegExpArray<>.

I'm fine with closing this PR if others prefer not to enable it 👍

[patak-cat]

I also don't know if the extra inconvenience is worthy here. I would vote to don't do merge this one at this point.

[sapphi-red]

Then, I'll close this one and #18798. I'll make a PR that extracts the fixes found in #18798 👍