[OpaquePointers] Fix translation of EnqueueKernel and block functions

[dwoodwor-intel]

This specifies the right parameter types for EnqueueKernel and for block
functions (with mangled names of the form {__,}block_invoke{,}{_kernel,}),
so that SPIR-V code is generated for these as expected. This fixes a
crash in the Intel OpenCL CPU backend, and likely other SPIR-V
consumers.

[dwoodwor-intel]

This patch is ready for review, but depends on #1799 (which also depends on D141008). I am seeing some test failures which don't seem to be specific to this change; they probably need to be fixed in #1799 when that is updated to be merged:

Failed Tests (2):
  LLVM_SPIRV :: extensions/INTEL/SPV_INTEL_device_side_avc_motion_esimation/subgroup_avc_intel_vme_image.cl
  LLVM_SPIRV :: image-unoptimized.cl

********************
Unexpectedly Passed Tests (1):
  LLVM_SPIRV :: transcoding/pipe_builtins.cl

[MrSidims]

LGTM, thanks!

[dwoodwor-intel]

I've rebased this on the current main branch now that the relevant fixes (and the test fix yesterday for #1885) are there. @jcranmer-intel also pointed out a few more block-related tests that need to be updated for opaque pointers, so I've updated those here too and fixed some bugs in my first implementation of the block part of this.

[MrSidims]

Restarting CI with new head