Migrate VerticalWhitespaceOpeningBracesRule to SwiftSyntax

## Summary

Convert VerticalWhitespaceOpeningBracesRule to use SwiftSyntax instead
of SourceKit for improved performance and better detection of empty
lines after opening braces.

## Key Technical Improvements

- **Enhanced trivia analysis** for accurate empty line detection after
  opening braces
- **Proper handling of closure "in" keywords** with context-aware
  detection
- **Improved correction logic** handling all newline types (LF, CR,
  CRLF) consistently
- **SwiftSyntax visitor pattern** replacing regex-based detection for
  better accuracy
- **Comprehensive token analysis** supporting all opening brace types
  (`{`, `[`, `(`)
- **Accurate position tracking** for violation start and end positions

## Migration Details

- Replaced `CorrectableRule, OptInRule` with
  `@SwiftSyntaxRule(correctable: true, optIn: true)`
- Implemented `ViolationsSyntaxVisitor` for detecting violations in
  token trailing trivia
- Implemented `ViolationsSyntaxRewriter` for correcting violations
  across different syntax contexts
- Added proper handling of closures, code blocks, arrays, and tuples
- Maintained exact position reporting for violation locations
- Preserved all existing test cases and rule behavior

Author: jpsim

CHANGELOG.md

@@ -42,6 +42,7 @@
   * `line_length`
   * `trailing_whitespace`
   * `vertical_whitespace`
+  * `vertical_whitespace_opening_braces`
   <!-- Keep empty line to have the contributors on a separate line. -->
   [JP Simard](https://github.com/jpsim)
   [Matt Pennig](https://github.com/pennig)