refactor: use n-args for all static combineLatest signatures

[cartant]

Description:

This PR uses the n-args mechanism for all of the static combineLatest's overload signatures.

As mentioned in a couple of other PRs: I realize that these sigs are deprecated, but we already have deprecated sigs in operators that use n-args, so, IMO, things are less confusing if n-args is useds wherever possible.

Further to that:

• The sheer number of overloads removed makes this source much easier to read and reason with.
• It will make it easier to manage the deprecation comments - after the breaking changes are done and v7 is ready, getting the deprecations sorted/fixed and relating them to the docs is something that needs to be done, IMO, as the deprecations confuse many devs.
• There has been some discussion about undeprecating some result selectors and - IMO - this is one API where the result selector is useful.
• Having the types behave differently for depreated and non-deprecated APIs is likely to confuse people.
• The Scheduler-related APIs that are deprecated are unlikely to be widely used.
• The ObservableInput-based type parameters are pretty unlikely to be specified explicitly anyway.
• If you're still not convinced, let me know and I'll come up with some more reasons, 'cause I really wanna get rid of those overload sigs. 🙂

Related issue (if exists): Nope

[benlesh]

Approved... but needs rebased after the other PR was merged.