[5.9][Macros] Don't apply member attribute macros to expanded members.

[hborla]

(cherry picked from commit 14e92b2)

• Explanation: The attached macro proposal states:

member attribute macros allow one to modify the member declarations that were explicitly written within the type or extension by adding new attributes to them

The implementation did not follow this, because it applied member attributes to other macro-expanded members. This change aligns the implementation with the proposal.

• Scope: Only impacts member-attribute macros that are composed with other macro roles that can add members to a type, e.g. member or peer macros.
• Issue: rdar://109217961
• Risk: Very low; this is a one-line change within the code path that expands member-attribute macros that checks whether the given member is in a macro expansion buffer relative to its parent.
• Testing: Added a test case.
• Reviewer: @ahoppen
• Main branch PR: [Macros] Don't apply member attribute macros to expanded members. #66258

[hborla]

@swift-ci please test