fixes#2140
Adds testing for SPIR-V 1.5 features:
* Adds a test for bitcasts between pointers and vectors of integers.
Note, SPIR-V 1.5 only supports bitcasts to vectors of two 32-bit
integers. Therefore, the SPIR-V 1.5 behavior will only be exercised on
devices with 64-bit pointers. The test will run on devices with 32-bit
pointers, but will instead bitcast to scalars.
* Adds a test for OpGroupNonUniformBroadcast with a dynamic index. Note,
this is not an exhaustive test, and only unsigned integer types are
tested, to avoid duplicating testing for cl_khr_subgroup_ballot.
