Make document symbol extensible

[st0012]

Motivation

By making DocumentSymbol request extensible, we can allow extensions to extend it. For example, users would be able to use document symbol feature to list Rails tests defined with test "name" too.

Implementation

I followed the common pattern for extension for this request as well. But for tests I added a test_extension helper to encapsulate some common boilerplate and essential cleanups.

Automated Tests

I added a new test case for the extension.

Manual Tests

[github-actions]

Benchmark results in seconds (slowest at top)

          textDocument/completion average: 0.239989 std_dev: 0.00549
          textDocument/diagnostic average: 0.05154 std_dev: 0.011734
          textDocument/definition average: 0.006179 std_dev: 0.003305
      textDocument/selectionRange average: 0.005126 std_dev: 0.000718
 textDocument/semanticTokens/full average: 0.003471 std_dev: 0.000876
   textDocument/documentHighlight average: 0.00328 std_dev: 0.000293
      textDocument/documentSymbol average: 0.003272 std_dev: 0.000375
            textDocument/codeLens average: 0.003165 std_dev: 0.000294
        textDocument/foldingRange average: 0.003052 std_dev: 0.000314
        textDocument/documentLink average: 0.003051 std_dev: 0.00027
textDocument/semanticTokens/range average: 0.002138 std_dev: 0.000233
               codeAction/resolve average: 0.00181 std_dev: 0.000175
               textDocument/hover average: 0.001748 std_dev: 0.000144
           textDocument/inlayHint average: 0.001738 std_dev: 0.00015
          textDocument/formatting average: 0.001103 std_dev: 0.000352
    textDocument/onTypeFormatting average: 0.001068 std_dev: 0.000123
          textDocument/codeAction average: 0.001015 std_dev: 0.000118


================================================================================
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

[vinistock]

Nice