Expand unknown function handling tests

Expand unknown function handling tests

Add tests for unknown device functions queried with both vkGetDeviceProcAddr
and vkGetInstanceProcAddr. Also loops enough times to exhaust the available
unknown function supply.

Had to fix the vk_layerGetPhysicalDeviceProcAddr in TestLayer to make the tests
pass.

MacOS currently skips tests which use vkGetInstanceProcAddr. This is due to the
need for unknown functions being lower priority and so do not warrent the time
needed to write the assembly necessary to resolve the issue fully.