[cxx-interop][serialization] resolve x-refs to instantiated/synthesiz…

[hyp]

…ed C++ iterator conformance operators

These x-refs might not be resolvable using regular lookup from the 'std' module as they could be instantiated/synthesized by the clang importer. Augment the lookup logic in that case to try clang importer lookup logic that is used during the conformance to the C++ iterator protocol.

I first tried to embed additional information during serialization to denote synthesized/instantiated operators, but that actually doesn't cover all operators: #74524 .

Fixes Cmake adopter build that breaks in merge modules using Android NDK and std::unordered_map implicitly generated conformances:

C:\Users\alex\AppData\Local\Temp\FirestoreDataConverter-6e2827.swiftmodule:1:1: error: reference to top-level declaration '==' broken by a context change; the declaration kind of '=='  changed since building '...', it was in 'CxxStdlib' and now a candidate is found only in 'Swift'
1 | CxxStdlib.==
  | |- error: reference to top-level declaration '==' broken by a context change; the declaration kind of '=='  changed since building 'FirebaseFirestore', it was in 'CxxStdlib' and now a candidate is found only in 'Swift'
  | |- note: the declaration was expected to be found in module 'CxxStdlib' at 'S:\b\arm64\Android.platform\Developer\SDKs\Android.sdk\usr\lib\swift\android\CxxStdlib.swiftmodule\aarch64-unknown-linux-android.swiftmodule'
  | |- note: or expected to be found in the underlying module 'std' defined at 'S:\android-ndk26\android-ndk-r26c\toolchains\llvm\prebuilt\windows-x86_64\sysroot\usr\include\c++\v1\module.modulemap'
  | |- note: the declaration was actually found in module 'Swift' at 'S:\b\arm64\Android.platform\Developer\SDKs\Android.sdk\usr\lib\swift\android\Swift.swiftmodule\aarch64-unknown-linux-android.private.swiftinterface'
  | |- note: a candidate was filtered out because of a type mismatch; expected: '(std.__ndk1.__hash_map_const_iterator<__hash_const_iterator<UnsafeMutablePointer<__hash_node<__hash_value_type<basic_string<CChar, char_traits<CChar>, allocator<CChar>>, FieldValue>, UnsafeMutablePointer<Void>>>>>, std.__ndk1.__hash_map_const_iterator<__hash_const_iterator<UnsafeMutablePointer<__hash_node<__hash_value_type<basic_string<CChar, char_traits<CChar>, allocator<CChar>>, FieldValue>, UnsafeMutablePointer<Void>>>>>) -> Bool', found: '(Builtin.NativeObject, Builtin.NativeObject) -> Bool'

[hyp]

@swift-ci please test

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@swift-ci please test

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@swift-ci please test source compatibility

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@swift-ci please test

[hyp]

@swift-ci please smoke test