Some games write from fragment shaders to an unexistant framebuffer
attachment or they don't write to one when it exists in the framebuffer.
Fix this by skipping writes or adding zeroes.
Update Sirit and its usage in vk_shader_decompiler. Highlights:
- Implement tessellation shaders
- Implement geometry shaders
- Implement some missing features
- Use native half float instructions when available.
Fix missing OpSelectionMerge instruction. This caused devices loses on
most hardware, Intel didn't care.
Fix [-1;1] -> [0;1] depth conversions.
Conditionally use VK_EXT_scalar_block_layout. This allows us to use
non-std140 layouts on UBOs.
Update external Vulkan headers.
