[5.7] Add API to enable or disable bare slash regex parsing

[ahoppen]

Depends on swiftlang/swift#59150

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• Explanation: [5.7][SwiftSyntax] Parse regex literals using a fallback lexer implemented in C++ swift#58998 enabled bare slash regex literals for SwiftSyntax parsing by default. This adds parameters to the SyntaxParser.parse functions that allow specifying whether bare slash regex literal parsing should be enabled.
• Scope: Parsing of SwiftSyntax trees
• Risk: Low
• Testing: Added regression tests
• Issue: rdar://93750821
• Reviewer: @rintaro on Add API to enable or disable bare slash regex parsing #448

[ahoppen]

swiftlang/swift#59150

@swift-ci Please test