Add support for local variable references

[nunosilva800]

Motivation

Closes #2642
Closes #3111

Implementation

1. Made the RubyIndexer::ReferenceFinder register on_local_variable_**_enter with the Prism::Dispatcher, and collect references to it while doing so.
2. RubyLsp::Requests::References now expects Prism::LocalVariable**Node and when the target is a RubyIndexer::ReferenceFinder::LocalVariableTarget, it collects references in the current ruby document and only under the parent of the target. This should limit the scope.
3. RubyLsp::Requests::Rename and RubyLsp::Requests::PrepareRename also expects Prism::LocalVariable**Node and follows same logic as the Reference request resolver to find and rename the local var.

Notes:

1. the usage of Prism::RequiredParameterNode to understand when a local var might be defined in a block argument - there might be better ways of doing this (as well as considering optional parameters?)

2. since the search for local var references is limited to the parent of target (what is under the cursor), when the var is inside a block, any reference to the var outside the block is not found. This is something that perhaps can be improved.

Automated Tests

Unit tests were added.

Manual Tests

Cannot use it manually... after following https://shopify.github.io/ruby-lsp/contributing.html#live-debugging I still see:

Which means something is missing from this PR 👀

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[nunosilva800]

@vinistock any clues on why I cannot test this with live debugging?
Also, what other examples of local var references/rename can you think of that should be tested? The current implementation is quite limited, but having other examples might guide me towards a better solution.