Add go to definition for classes and modules

[vinistock]

Motivation

Closes#199

Closing the related issue since the exploration is complete. This PR adds go to definition for classes and modules, which is currently what's covered in the index.

Implementation

The idea is to find constant/constant path nodes and look for them inside the index and then allow jumping to those.

If the project uses Sorbet, we avoid returning locations for classes and modules that are defined inside the project - since Sorbet can find those even for typed: false files. But we still return all results for definitions from gems, which should provide a nice merged experience.

Automated Tests

Added a test for this.

Manual Tests

1. Boot the LSP on this branch
2. Try to go to the definition of a class defined in the Ruby LSP itself (e.g.: EventEmitter)
3. Verify you jump directly to it, without having multiple options (this is coming from Sorbet only)
4. Try to go to definition of a class defined in a gem (e.g.: SyntaxTree::Const)
5. Verify you get both RBIs and the actual gem source as results

[github-actions]

Benchmark results in seconds (slowest at top)
textDocument/completion average: 0.305521 std_dev: 0.006352
textDocument/diagnostic average: 0.048978 std_dev: 0.011798
textDocument/definition average: 0.006183 std_dev: 0.003456
textDocument/selectionRange average: 0.00484 std_dev: 0.00061
textDocument/documentHighlight average: 0.002988 std_dev: 0.000323
textDocument/codeLens average: 0.002953 std_dev: 0.000268
textDocument/documentLink average: 0.002935 std_dev: 0.000201
textDocument/semanticTokens/full average: 0.002932 std_dev: 0.000303
textDocument/foldingRange average: 0.002906 std_dev: 0.0002
textDocument/documentSymbol average: 0.002883 std_dev: 0.000134
textDocument/semanticTokens/range average: 0.001933 std_dev: 0.000165
codeAction/resolve average: 0.001714 std_dev: 0.000167
textDocument/hover average: 0.001655 std_dev: 0.000109
textDocument/inlayHint average: 0.001605 std_dev: 0.000155
textDocument/formatting average: 0.000992 std_dev: 0.000231
textDocument/onTypeFormatting average: 0.000984 std_dev: 0.000118
textDocument/codeAction average: 0.000963 std_dev: 0.000109
================================================================================
Comparison with main branch:
textDocument/semanticTokens/full unchanged
textDocument/semanticTokens/range unchanged
textDocument/documentSymbol unchanged
textDocument/foldingRange unchanged
textDocument/formatting unchanged
textDocument/diagnostic unchanged
textDocument/documentLink unchanged
textDocument/inlayHint unchanged
textDocument/selectionRange unchanged
textDocument/documentHighlight unchanged
textDocument/hover unchanged
textDocument/codeAction unchanged
textDocument/onTypeFormatting unchanged
codeAction/resolve unchanged
textDocument/completion unchanged
textDocument/codeLens unchanged
textDocument/definition unchanged
================================================================================
Missing benchmarks:
RubyLsp::Requests::ShowSyntaxTree