[DirectX] Add DXILRemoveUnusedResources pass (#200965)
Adds `DXILRemoveUnusedResources` pass that scans the module and removes
any resource that is not used. It means that it removes calls to
`dx_resource_handlefrom{implicit}binding` whose return value is either
not used at all, or it is saved to a global variable that does not have
external linkage and is not used anywhere else in the module.
This pass needs to run before implicit resource binding assignment pass.
The test `unused-resources-impl-binding.ll` makes sure the implicit
binding assignments are not affected by the unused resources.
Since we have many tests that are initializing resources without
actually using them, an internal option
`-disable-dxil-remove-unused-resource` has been added to `llc` so we can
keep these tests simple without adding extra code to artificially use
each resource.
Depends on #200312
Fixes #192524
