C#: Unwrap parentheses in pattern matching comparator

[knutwannheden]

Motivation

The C# pattern matcher (PatternMatchingComparator) did not ignore optional expression parentheses, so a pattern like Console.WriteLine("hello") would fail to match Console.WriteLine(("hello")), and a parenthesized pattern (x + 1) wouldn't match the unparenthesized x + 1. The JavaScript comparator already handles this via an unwrap() step — this brings parity to C#.

Summary

• Added a non-generic Parentheses interface (extending Expression) with an InnerTree property, so Parentheses<T> can be type-checked and unwrapped without reflection
• Parentheses<T> now implements the non-generic Parentheses interface
• PatternMatchingComparator.UnwrapParentheses() recursively strips Parentheses wrappers using a simple while (node is Parentheses p) loop
• Both pattern and candidate are unwrapped at the top of MatchNode and in the fast-reject path in CSharpPattern.Match

Test plan

• MatchesConcreteArgThroughParentheses — pattern without parens matches candidate arg wrapped in parens
• ParenthesizedPatternMatchesUnparenthesized — parenthesized pattern (x + 1) matches x + 1
• All 108 existing PatternMatchTests pass (no regressions)