Add tests for EXT_external_objects_win32 with a D3D12 producer
This adds a test framework and several tests, based on the Vulkan tests for EXT_external_objects_fd
. A few of the tests arbitrarily use import-by-name, and at least one test validates the fence value behaviors.
These tests all pass on my Mesa implementation in mesa!17446 (merged).
Edited by Jesse Natalie