Properly handle methods for definition, completion and hover

[vinistock]

Depends on #898 and #1333

Use the index to provide go to definition for methods.

Might depend on exploring using a control flow graph (CFG) to implement reaching definitions. While we do not provide typechecking, using reaching definitions might allow us to be more precise.

For example

a = "something"
# We know that `a` is a string because it's a literal, so we know 100% sure this has to be
# String#upcase. If we have an implementation of reaching definitions, we can make this work
a.upcase

Checklist

• Attributes. The LSP protocol has special types for them, so we should create a separate index entry
• Taking new invocations to initialize. For completion, it's actually the opposite, we need to use the signature for initialize, but complete to new
• Method aliases through alias_method and alias

[github-actions]

This issue is being marked as stale because there was no activity in the last 2 months

[Kyrluckechuck]

Just bumping this since it's not stale and I don't want it marked as closed without being formally acknowledged! 😅

[andyw8]

It's not usable yet, but a first step towards this was merged today: #1043