d: Enable private member access for __traits

d: Enable private member access for __traits

The following traits can now access non-public members:
 - hasMember
 - getMember
 - getOverloads
 - getVirtualMethods
 - getVirtualFuntions

This fixes a long-standing issue in D where the allMembers trait would
correctly return non-public members but those non-public members would
be inaccessible to other traits.

Reviewed-on: https://github.com/dlang/dmd/pull/12135

gcc/d/ChangeLog:

	* dmd/MERGE: Merge upstream dmd 3a7ebef73.