This new optimization passes determines the required capabilities for a
module, and strips unneeded capabilities.
This means if some dead-code uses a capability, it won't be added as a
requirement for the module anymore.
This interacts with `[[vk::ext_capabilities]]` and
[[vk::ext_extension]]` attributes, as the extension/capability they
declare could be stripped if not required.
Still markes as draft for now as there are inconsistencies with debug
instruction I need to figure out:
- if 2 DebugScope are generated, SPIRV-Tools squash them into 1.
- seems like we started to generated the wrong ones, but test didn't saw
the 2 conflicting scopes, only checked the first one.
da36098644