Unit test for cuBLAS_missing_functions

**Is your feature request related to a problem? Please describe.**

This batched BLAS functionality should be tested, as discussed in #2486

**Describe the solution you'd like**

Standalone unit test.

Would be good to write at the "missing function" level if practical so that the same code can be used to test other back end implementations.

**Describe alternatives you've considered**

Use vendor libraries, but they aren't implemented.

**Additional context**