Feat(SwiftRefactor): Implement InvertIfCondition refactoring

[rickhohler]

Description

This PR implements the InvertIfCondition refactoring action, which supports SourceKit-LSP #2408.

Transformation:

if !x {
  foo()
} else {
  bar()
}
// becomes:
if x {
  bar()
} else {
  foo()
}

Detailed Design

• Adds InvertIfCondition provider to SwiftRefactor.
• Criteria (Strict Scope):
  • Input must be an IfExprSyntax.
  • Must have an else block (CodeBlock).
  • Must have exactly one condition.
  • Condition must be negated (PrefixOperatorExpr with !).
• Logic:
  • Unwraps the negation (!condition -> condition).
  • Swaps the body and elseBody.
  • Preserves trivia (comments/whitespace) by swapping leading/trailing trivia between the blocks.

Fixes

Addresses logic for swiftlang/sourcekit-lsp#2408.

Pre-PR Checklist

• Code builds and passes tests.
• Ran swift-format.
• Added unit tests in InvertIfConditionTest.swift.