Other implementations of the symbol graph format use zero-based indices
for source locations, which causes problems when combined with clang's
current one-based indices. This commit sets ExtractAPI's symbol graph
output to use zero-based indices to align with other implementations.
rdar://107639783
Refactor visitation for C++ record children by following the Visitor's CRTP.
Expand VisitCXXField, VisitCXXMethod for non-templates and introduce VisitCXXConstructor, VisitCXXDestructor.
Handle relationships by finding the parent's Record via USR from DeclContext.
Depends on D158029
Reviewed By: dang
Differential Revision: https://reviews.llvm.org/D158031
Reintroduce D153557 with fix for use-after-free from f4de606ef271 and minor changes.
Reviewed By: dang
Differential Revision: https://reviews.llvm.org/D157007
