[PSA] Conversion to LLVM passes now emit opaque pointers by default

Hello everyone!

As outlined in [PSA] In-tree conversion passes can now be used with LLVM opaque-pointers; Please switch your downstream projects!, it has now been two weeks since the initial anncouncement. Therefore opaque pointers have now been turned on by default in all conversion to LLVM passes.

Downstream users of LLVM passes who have not yet switched to opaque pointers may now experience breakage in the form of verifier errors, assertions or similar. Users who exclusively use upstream passes should not experience a difference except in LLVM Dialect output.

To switch back to typed pointers you must either set useOpaquePointers to false within the pass options of conversion passes or set useOpaquePointers to false within the LowerToLLVMOptions struct used to construct a ´LLVMTypeConverter`.

For precise instructions how to migrate to opaque pointers see the first PSA

The current plan to remove typed pointer support in-tree entirely in exactly 4 weeks from now remains.