Add C# 11 raw string literal support

[Copilot]

Implementation Plan for Raw String Literals (C# 11)

Following the plan in docs/plans/raw-strings/plan.md and tracking progress in docs/plans/raw-strings/todo.md.

All Phases Complete ✅

Code Review Feedback ✅

• [x] Add comprehensive brace escaping tests
• [x] Refactor state management - remove CurrentQuotes overloading
• [x] Use local variables for temporary scanning state
• [x] Implement correct brace escaping logic (odd/even group counting)
• [x] Fix test expectations for brace escaping

Implementation Complete! 🎉

Status: All 601 tests passing!

Raw string literal scanning is now fully functional for:

• ✅ Single-line and multi-line non-interpolated raw strings ("""text""")
• ✅ Single-line interpolated raw strings with holes ($"""text {expr}""", $$"""text {{expr}}""")
• ✅ Multi-line interpolated raw strings with holes ($"""\ntext {expr}\n""")
• ✅ Nested string combinations (raw in raw, raw in regular, regular in raw)
• ✅ Complex expressions in holes (brackets, switch expressions with braces)
• ✅ Brace escaping in interpolated raw strings ($$"""{{{{literal}}}}""", $$"""{{{x}}}""")

Architecture: All scanning processes characters one at a time without relying on buffer assumptions, making the scanner ready for potential streaming/chunked input support. The implementation uses a local variable (rawQuoteOrBraceCount) for temporary state tracking instead of overloading fields in InterpolationState, improving code maintainability.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Implement support for raw string literals (C# 11)</issue_title> <issue_description>Add support for raw string literals, that were introduced with C# 11 by creating a PR that targets the existing rawstring branch (when it will be merged)

• Implement the feature according to the plan in docs/plans/raw-strings/plan.md
• Track the phases of the implementation in docs/plans/raw-strings/todo.md. A phase is complete if all tests are passing. Create a Git commit for each phase before moving on to the next phase.

</issue_description>

<agent_instructions>See instructions in issue #55</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes atifaziz/CSharpMinifier#55

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