Let's rewrite the test harness

[cbezault]

This change is mostly cleanups, though it brings us more in line with libcxx's testing format in terms of style and functionality.

I also tried to decrease the size of the TestConfig and STLTest objects as much as possible since those are pickled and communicated to the worker processes via IPC. On my machine I saw a ~20% decrease in testing time with this change (~75mins to ~60mins), we'll see if that holds true on the test machines.

[cbezault]

@rpjohnst If you could make sure I didn't break your edg_drop machinery that would be much appreciated.

[StephanTLavavej]

I encountered one test failure because my repo root, S:\GitHub\STL, combined with an exceptionally long libcxx path, combined with /analyze's emission of a long-named XML file, exceeded the MAX_PATH limit. This made me realize that /analyze is emitting XML files that we never, ever want. I've pushed a commit to change all occurrences of plain /analyze to /analyze:autolog- which will still emit the warnings we want, but not the XML files. With this change, everything passes for x86:

Testing Time: 6095.88s
  Skipped          :   358
  Unsupported      :  1895
  Passed           : 22678
  Expectedly Failed:  1015

Same for x64:

Testing Time: 5919.71s
  Skipped          :   358
  Unsupported      :  3247
  Passed           : 21326
  Expectedly Failed:  1015

This doesn't change our /analyze:only options. I'll file an issue about that.

[CaseyCarter]

I'm totally breaking @StephanTLavavej's 17-attack PR merge combo. 🐼

[CaseyCarter]

All good now!

[StephanTLavavej]

Thanks for this overhaul, improving test performance! This will both increase maintainer/contributor productivity 🚀 and decrease our costs 🤑.