[5.9] Fix two memory corruption bugs in SwiftSyntax

[ahoppen]

This is a slightly less risky version of #1708

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• Explanation: This PR fixes three different potential memory corruption bugs when modifying SwiftSyntax nodes
  • SyntaxData.forRoot takes a RawSyntax, which holds a reference to its SyntaxArena but RawSyntax doesn’t retain its arena. We were already taking care of this in multiple places by adding a withExtendedLifetime for the arena around it but missed a case in SyntaxData.replacingSelf. Add withExtendedLifetime here as well.
  • The replacingChild function took a RawSyntax, which again doesn’t retain its arena. When changing any syntax node’s child, we have a value, which is a Syntax node but all we did in the setter was to pass value.raw into replacingChild. This left an opportunity for the optimizer to deallocate the Syntax node (and thus it’s arena) before the call to replacingChild because all we needed from hat node was the RawSyntax. To fix this, add another version of replacingChild that takes a SyntaxData (which does retain the arena) and use that instead.
  • SyntaxArena.rewrite passed a new SyntaxArena to replacingSelf, but replacingSelf expected to be passed the arena in which rewritten was allocated.
• Scope: Functions that modified syntax nodes
• Risk: Low, this effectively PR only adds withExtendedLifetime calls
• Testing: Ran unit tests and verified that swift-format doesn’t regress in performance
• Issue: rdar://109860357
• Reviewer:

[ahoppen]

@swift-ci Please test