Summary of Changes

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This pull request significantly enhances the WhitespaceFormatter by implementing a new feature for folding labeled expressions and arguments. The primary goal is to improve code readability and reduce vertical space by intelligently collapsing arguments onto fewer lines, specifically by removing newlines between colons and their corresponding values, and between expressions and trailing commas. This is achieved through the introduction of specialized syntax visitors and rewriters, along with a new configurable option to manage this formatting style.

Highlights

• New Argument Folding Feature: Introduced the ability to fold labeled expressions and arguments, removing newlines between colons and values, and between expressions and trailing commas for more compact code.
• New Syntax Processors: Added ArgumentCalculator (a SyntaxVisitor) to identify optimal positions for folding, and TokenFolder (a SyntaxRewriter) to apply the actual whitespace adjustments.
• Enhanced VerticalRewriter: The VerticalRewriter protocol's align function was made more flexible by allowing an optional separator, enabling precise control over whitespace insertion during folding.
• New Configuration Option: A foldArguments boolean option was added to WhitespaceOptions, allowing users to enable or disable this new formatting behavior, with a default value of true.
• Comprehensive Testing: New unit tests in ArgumentFoldingTests.swift were added to ensure the correct functionality of both labeled and unlabeled argument folding scenarios.