[PATCH vkd3d 4/5] tests: Add a test for texture load instructions.

[Matteo Bruni]

Signed-off-by: Matteo Bruni <mbruni at codeweavers.com>
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With the caveat that I'm not really well-versed in d3d12.

Creating a separate descriptor heap and table for each texture seems
questionable but probably good enough for these tests...