Include function argument names as part of "function-arguments" for introspector API

[oliverchang]

We discussed this offline, but it would be very nice to get the function arg names returned in /api/far-reach-but-low-coverage as part of the existing "function-arguments" value.

[DavidKorczynski]

We extract this for C/C++ in the frontend

fuzz-introspector/frontends/llvm/lib/Transforms/FuzzIntrospector/FuzzIntrospector.cpp

Line 1072 in 13ba8d5

FuncWrap.ArgNames.push_back(A.getName().str());

However, when expecting the output the values are all empty strings. It could be this is gone at the point we extract them. I need to investigate a bit more -- it may be we need to open up for a way to inspect these values at a different stage of the compilation process. Perhaps, we need to extract it from the source code itself, which we can do since we do know the location of the functions we're analysing.