Split atomics tests into heap/root types (#3526)

To test the flag indicating support for 64-bit atomics on heap
resources, the groupshared and raw tests are here altered to use root
descriptors. An nearly identical raw buffer test is kept for heap
testing and the typed resources, requiring heap support implicitly, is
unaltered. 32-bit testing, encompassing typed resources and all else,
are kept in the typed variants

Renamed a few things to make the names less confusing.

Author: Greg Roth