feat(LimitedCollection): export LimitedCollection

[PanSzelescik]

Please describe the changes this PR makes and why it should be merged:

Closes #4274, I don't know why it isn't exported

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating
• This PR changes the library's interface (methods or parameters added)

[ckohen]

Please remove the @private docstring in the file

[PanSzelescik]

Please remove the @private docstring in the file

Removed

[PanSzelescik]

Should I add typings in Collections region?

[SpaceEEC]

There is still the issue with implicitly creating new instances of LimitedCollection through its methods, e.g. clone, filter.
TS will say those are LimitedCollections, but they actually are Collections.
(Creating new LimitedCollections is not possible without modifying Collection and thinking of a way to derive new arbitrary child instances)

I don't know of a way to make TS aware of Symbol.species and overwriting all methods to specify that actually a Collection is returned is error prone and tedious.

So I suppose 🤷

[SpaceEEC]

Yeah, moving the declaration for LimitedCollection would be nice, @PanSzelescik.

[iCrawl]

This needs a rebase.