Add BUILD_BVT mode for ctest running as a GHA

[walbourn]

A subset of the test suite should be buildable and run as a GitHub action. The challenge is that it needs to leverage WARP using a headless render target since there's no guarantees of GPU support in a GHA runner.

[walbourn]

The only command-line tests currently that would work in the cloud are headertest and wavtest.

Proposal:

• Add command-line test 'DDSWICTest' to do an exhaustive validation of DDSTextureLoader, WICTextureLoader, and ScreenGrab

• Add a command-line test 'APITest' that does basicaly 'invalid arg' and unit-test style tests of the components with a NULL device and not any rendering