Subgroups tests - need to modify kernel names for easier debugging

Per comment https://github.com/KhronosGroup/OpenCL-CTS/pull/1074#discussion_r554049049:

> Could you rename the kernel function names to fully spell our the builtin function being tested? I believe this would provide useful when grep-ing compilation logs, for example.

Start with the subgroup tests and the kernel function names discussed in pull request #1074, especially the linked discussion. Trace each name to the builtin function it tests, then rename the kernels so the builtin is fully spelled out and confirm compilation logs expose the intended names.

Written by the indexing model from the issue text.