Improve DSC expression grammar speed

[SteveL-MSFT]

PR Summary

Small improvement to DSC expression parsing speed.

Before change: average speed: 3147 bytes/ms

After change: average speed: 3233 bytes/ms

[Copilot]

Pull request overview

Small performance optimization to the tree-sitter grammar for DSC expressions. Makes regex patterns greedy (longest-match) since tree-sitter's lexer already prefers longest-match, removes redundant alternations, and inlines several helper rules to reduce parse tree overhead.

Changes:

• Added an inline declaration for _booleanLiteral, _argument, _quotedString, and _expressionString so they are expanded at compile time.
• Simplified regexes for escapedStringLiteral and stringLiteral to greedy patterns (/.*/ and /[^\[][\s\S]*/).
• Removed the redundant |\n branch in the string regex (already covered by [^']).