[d3d9] Handle remaining edge cases of Discard & Lockable

[K0bin]

A bunch of edge cases we weren't handling properly. This is gonna need some testing.

In theory we could also use VK_STORE_OP_DONT_CARE for discardable depth stencil surfaces but I don't think that's worth the additional complexity. Tracking the load op is already a bit of a mess. Games don't really use discardable depth stencil surfaces all that much and it would only help tilers anyway as far as I know.

[Blisto91]

Tested with 9 random d3d9 games of varied engines so far, not seen any issues. Tested on Nvidia.

[misyltoad]

Looks fine