Fix incorrect extend T::Helpers for foreign annotations

[KaanOzkan]

Ran into some gems that specify # @private which was causing us to insert extend T::Sig.

Also a small refactor Annotations -> Annotation

[st0012]

I think we can put multiple cases together like:

Suggested change

	when "@abstract"
	true
	when "@interface"
	true
	when "@sealed"
	true
	when "@final"
	true
	when /^@requires_ancestor: /
	true
	when "@abstract", "@interface", "@sealed", "@final"
	true
	when /^@requires_ancestor: /
	true

Regexp and string matches can be put together too, but I think giving the regexp match its own condition can make it easier to spot.

[st0012]

Same as the above.

[st0012]

Is it worth memoizing this value?

[KaanOzkan]

Do you mean annotations or the resulting array from select?

[st0012]

The resulting array

[Morriar]

Risky if @comments change?

[st0012]

Should it change if we already started the translation?

[Morriar]

Should they: no. Can they?

I'm generally uneasy with memoization based on array attributes because they can change even with an attr_reader and there is no obvious cut point to freeze them.

[st0012]

That's fair and I'm fine with not memorizing as it doesn't seem to be a performance bottleneck anyway 👍