[XRay][tools] Add option to llvm-xray extract to symbolize functions

Summary:
This allows us to, if the symbol names are available in the binary, be
able to provide the function name in the YAML output.

Reviewers: dblaikie, pelikan

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32153

llvm-svn: 300624