This is the first part of my partial presentation support patchset. Only the tests and minor implementation changes.
Actual implementation will follow in multiple parts: minor refactoring of swapchain backbuffers, then actual implementation for dirty rectangles (with limitations), then limitations will be removed step-by-step, at the very end the scroll will be implemented.
I had to mark many new tests as "flaky" (not "todo"). They are not actually flaky, they are perfectly stable on both Windows 8 RTM and one of the latest Windows 11 Canary builds. But since they check multiple pixels and some of them match, this causes the "failures". I saw no better solution which didn't involve new APIs in `wine/test.h`. Their number will drop in the next MRs to 0.