feat: Add Elixir moduledoc support

[ianlewis]

Description:

Add Elixir moduledoc support and refactors the LanguageConfig to reuse some config. Adds support for multiple multi-line comment configurations per language.

Related Issues:

Fixes: #1546

Checklist:

• Review the CONTRIBUTING.md documentation.
• Add a reference to a related issue in the repository.
• Add a description of the changes proposed in the pull request.
• Add unit tests if applicable.
• Update documentation if applicable.
• Add a note in the CHANGELOG.md if applicable.
• Sign the Google CLA.

[codecov]

Codecov Report

Attention: Patch coverage is 94.59459% with 2 lines in your changes missing coverage. Please review.

Project coverage is 76.07%. Comparing base (6449e88) to head (32bfe4b).
Report is 1 commits behind head on main.

Files	Patch %	Lines
internal/scanner/scanner.go	93.33%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1548      +/-   ##
==========================================
+ Coverage   75.85%   76.07%   +0.22%     
==========================================
  Files          17       17              
  Lines        1147     1158      +11     
==========================================
+ Hits          870      881      +11     
  Misses        201      201              
  Partials       76       76              

Files	Coverage Δ
internal/scanner/state.go	0.00% <ø> (ø)
internal/todos/todos.go	99.20% <100.00%> (+0.02%)	⬆️
internal/scanner/scanner.go	71.68% <93.33%> (+0.60%)	⬆️