SwiftExtract: separate protocol requirements from default implementations and extension members

[Hokila]

Summary

Fixes swiftlang#891 by distinguishing genuine protocol requirements from default implementations in SwiftExtract (at requirement collection time) rather than deduplicating during code generation:

• Defer protocol extensions: Unconstrained protocol extensions are collected after all nominal declarations have been analyzed, guaranteeing that all protocol requirements are known before matching default implementations.
• Separate storage in ExtractedNominalType:
  • methods and variables exclusively store true protocol requirements declared in the protocol definition.
  • Default implementations provided by protocol extensions are recorded in protocolDefaultImplementations.
  • Non-requirement extension methods and variables are recorded in protocolExtensionMethods / protocolExtensionVariables.
• Requirement satisfaction matching:
  • Implemented ExtractedNominalType.satisfiesProtocolRequirement(candidate:requirement:) and findProtocolRequirement(satisfying:in:).
  • Matches based on function/property name, argument labels, parameter types, conventions, and result types, while ignoring parameter internal names and default argument expressions.
  • Allows non-throwing implementations to satisfy throwing requirements while preserving the throwing requirement on the protocol.
• Inherited protocol deduplication:
  • In allProtocolRequirementMethods, deduplicate refined requirements across inherited protocols using breadth-first traversal and satisfiesProtocolRequirement.
• Comprehensive testing:
  • Added 8 regression test cases in JNIProtocolTests covering unique existential box dispatch thunks, Java methods, differing parameter names, overloads, non-throwing default implementations, callback wrappers, non-requirement extension methods, and get-only property setters.

Testing

• swift test --filter JNIProtocolTests (25/25 passed)
• swift test --filter SwiftExtractTests (91/91 passed)
• swift test --filter JExtractSwiftTests (607/607 passed)
• xcrun swift-format lint --configuration .swift-format clean