SPIR-V validation understands VK_EXT_scalar_block_layout

SPIR-V validation understands VK_EXT_scalar_block_layout

Refactor SPIR-V validator options into own struct and header

Shader build options now record scalar layout flag.

Shader build options can yield a validator options object.

Update SSBO and UBO layout tests to tell validation when they are
using scalar layout.

Update fetch_sources.py to include GitLab SPIRV-Tools supporting
validation of scalar block layout.

Remaining validation failures:
- FPRoundingMode checks are not sensitive to capabilities in
  SPV_KHR_float_controls

Components: Vulkan
Affects:
dEQP-VK.ssbo.*
dEQP-VK.ubo.*

Change-Id: I4449b58f8c33c82eea8965847059fdeb22806876