Add brace matching for sigil delimiters

[mkaput]

Summary

Add brace matching support for sigil delimiters so that when the cursor is positioned near a sigil's opening delimiter, its matching closing delimiter is highlighted.

Elixir sigils support various delimiter pairs:

• ~s(...), ~r(...) - parentheses
• ~s[...], ~r[...] - brackets
• ~s{...}, ~r{...} - braces
• ~s<...>, ~r<...> - angle brackets
• ~s|...|, ~r|...| - pipes
• ~s/.../, ~r/.../ - slashes
• ~s"...", ~r"..." - double quotes
• ~s'...', ~r'...' - single quotes

Current Behavior

Currently, sigils are tokenized as a single EX_SIGIL token containing the entire sigil including its delimiters and content:

EX_SIGIL: ~r/pattern/i

As a single token, there's no way to match the opening / with the closing /.

Desired Behavior

When the cursor is near a sigil's opening delimiter, the matching closing delimiter should be highlighted. For example, in ~r/pattern/, positioning the cursor at the first / should highlight the second /.

Complexity considerations:

• Symmetric delimiters (|, /, ", ') use the same token for open and close
• Asymmetric delimiters ((), [], {}, <>) need distinct open/close tokens
• IntelliJ-Elixir handles this with LINE_PROMOTER/LINE_TERMINATOR tokens

Reference

IntelliJ-Elixir implementation:

• Paired.java - includes LINE_PROMOTER/LINE_TERMINATOR pair
• The lexer uses states like SIGIL, GROUP, etc. to track context

Acceptance Criteria

• Sigil opening delimiters match closing delimiters for all delimiter types:
  • () pairs
  • [] pairs
  • {} pairs
  • <> pairs
  • || pairs
  • // pairs
  • "" pairs
  • '' pairs
• Heredoc-style sigils (~s"""...""") also work (may depend on Add brace matching for heredocs #54)
• Sigil modifiers are still properly recognized
• Parser tests continue to pass
• Syntax highlighting continues to work correctly

Notes

This is a larger undertaking than heredoc support due to the variety of delimiter types. Consider implementing incrementally, starting with the most common delimiters.