Modify YardDoc listener to create RBS signatures

[KaanOzkan]

Relies on Shopify/rbi#420

Motivation

This listener is responsible for identifying RBS signatures from method comments exported from gems.

Implementation

Duplicated YARD comment retrieval and then small processing

Tests

Added

[Morriar]

Shoudn't we also change the Yard listener to not create a comment?

I'm not sure if we want to have both listeners tbh, maybe just one that create either a RBI::Comment or a RBSSig?

btw, maybe RBI::SigComment would be better? Not sure.

[KaanOzkan]

Shoudn't we also change the Yard listener to not create a comment?

I opted for skipping it in RBI::Printer instead. Also we have separation of concerns.

I'm not sure if we want to have both listeners tbh, maybe just one that create either a RBI::Comment or a RBSSig?

YARD listener is doing quite a bit, I like having 2 separate. But it's slower since we go through the comments again. If we want performance we can combine them.

[Morriar]

Considering #: -> void, we already ignore the # fine, we also skip the :, but we should strip the result before passing it to RBSSig.new.