R1:deea2f01f5d2

Allow unit tests to have arbitrarily long names (>255 characters)

Summary:
Depends on D20179. Ref T13088. See PHI351. See PHI1018. In various cases, unit tests names are 19 paths mashed together.

This is probably not an ideal name, and the test harness should probably pick a better name, but if users are fine with it and don't want to do the work to summarize on their own, accept them. We may summarize with "..." in some cases depending on how this fares in the UI.

The actual implementation is a…