[ClangImporter][Swiftify] merge importBoundsAttributes with importSpanAttributes and support lifetime bounds for __counted_by
- [ClangImporter] Merge paths for std::span and __counted_by
importBoundsAttributes and importSpanAttributes are merged into a single
function named swiftify. This allows us to not have to duplicate the
effort of attaching _SwiftifyImport macros, but is also necessary to
allow importing a function with both __counted_by and std::span types.
- [ClangImporter] Enable parsing bounds safety attributes in C++
This allows combining __counted_by and std::span for safe interop.
Previously we disabled this in C++ mode due to issues when bounds
attributes occurred directly or indirectly in templated contexts, but
this has now been resolved on the clang side.
- [Swiftify] Emit Span for counted_by return values with lifetime info
__counted_by return values with .lifetimeDependence are now mapped to
Span instead of UnsafeBufferPointer. Also fixes bug where std::span
return values would map to Span even if lifetime dependence info was
missing.
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