Test exact sampling with linear filtering over a solid color

Test exact sampling with linear filtering over a solid color

This commit adds new test variants for exact sampling cases using solid
color textures instead of gradients, paired with samplers configured to
use linear filtering. The implementation of linear filtering may incur
precission losses but they should be minor and we should get the exact
same color when converting back to the original image format.

New tests:
dEQP-VK.pipeline.sampler.exact_sampling.*.solid_color.*

Affected tests:
dEQP-VK.pipeline.sampler.exact_sampling.*

Components: Vulkan
VK-GL-CTS issue: 2226

Change-Id: I71800172b4826860070f5aee9bccca694557f062