Add Vulkan framework enums for SPIR-V 1.4

Add Vulkan framework enums for SPIR-V 1.4

Currently, no version of Vulkan requires support for SPIR-V 1.4.
Use of SPIR-V 1.4 requires an extension.

Therefore helper function getMaxSpirvVersionForAsm still returns at most
SPIRV_VERSION_1_3.  The affected SPIR-V 1.4 tests are added, but should
not run because they should be "not supported".

Update external/fetch_sources.py to get preliminary SPIRV-Headers
and SPIRV-Tools support for SPIR-V 1.4.  Relies on gitlab-prelim-rc12
tags those Gitlab repos.

Components: Vulkan

Affects:
dEQP-VK.spirv_assembly.instruction.compute.spirv_version.1_4_compute
dEQP-VK.spirv_assembly.instruction.graphics.spirv_version.1_4_vertex
dEQP-VK.spirv_assembly.instruction.graphics.spirv_version.1_4_tesselation_evaluation
dEQP-VK.spirv_assembly.instruction.graphics.spirv_version.1_4_tesselation_control
dEQP-VK.spirv_assembly.instruction.graphics.spirv_version.1_4_geometry
dEQP-VK.spirv_assembly.instruction.graphics.spirv_version.1_4_fragment

VK-GL-CTS issue: 1636

Change-Id: Ia1da3255d55b2db4d4a7c8ff5e4ef53057e96dd0