Test negative value conversion to b10g11r11 float format.

Test negative value conversion to b10g11r11 float format.

Added a test that verifies negative values are converted
correctly to b10g11r11 packed float format. These values
need to be clamped to zero.

Also moved texture subgroup LOD Amber test files to
a common directory shared by the new test.

VK-GL-CTS Issue: 2271

New tests:

dEQP-VK.texture.conversion.b10g11r11-negative-values

Components: Vulkan
Change-Id: Ide52844f1467f1e7c23d7510ba951d398a8814ac