[clang-doc] Serialize inherited attributes and methods

clang-doc now serializes the inherited attributes and methods, not only the name of the base class.
All inherited are tracked, if B:A and C:B, info of A is included in C.
This data is stored in attribute Bases in a RecordInfo.
Previously tracked inheritance data, stored in Parents and VParents, hasn't been removed to reduce review load.

Differential revision: https://reviews.llvm.org/D66238

llvm-svn: 369075