Avoid stack allocation for test_requires_unified_shared_memory_heap*

[tob2]

Some (pseuo)USM implementations allocate memory in a special memory section that permits either direct memory access (DMA) from the device or on-access migration. In that case, stack and static memory may or may not be accessible.

This pull request changes the test_requires_unified_shared_memory_heap{,_map,_is_device_ptr}.{c,F90} testcases such that only heap memory is used on the device. The existing test_unified_shared_memory*.* testcases handle the other variants.

@nolanbaker31 @spophale @jrreap @krishols @mjcarr458 – please review

This is a consistency fix – permitting a partial pass with pseudo USM. For full USM, kernel + hardware support is required to access all memory. I some (but not all) post-Pascal Nvidia cards permit to access all memory and, if I understood it correctly (big “if”), AMD cards since VEGA support accessing all memory in principle, but effectively, only gfx90a (MI 200 series) permits fast access and has proper.