Fixes#17014
Even if our depth-testing-equal heuristic believes that the game needs
lower depth resolution.
This removes some depth-fighting artifacts (that are present on the real
PSP, but nice to avoid) in Outrun, Split/Second and Cars: Race-o-Rama -
essentially reverting these to the behavior we had before the heuristic.
(The heuristic is good though - it means less compat.ini hacks going in
the other direction).
In the case of Outrun, this relies on two passes that pass exactly the
same vertex coordinates twice resulting in the exact same final
geometry. This is actually guaranteed by the spec if the vertex math is
exactly the same and "invariant" is set on the position output, though
I guess you never know.. Haven't seen any issues at least.
Also sneak in disabling some validation messages from using extra Vulkan
validation layers other than the default.
[how]
1. use comment instead of unnecessary logic comparison
2. remove some useless code
3. move some implemention code from header to source
4. some more assert
