[mlir][Transform] Add support to drive conversions of func to LLVM with TD

This revision adds a `transform.apply_conversion_patterns.func.func_to_llvm` transformation.

It is unclear at this point whether this should be spelled out as a standalone transformation
or whether it should resemble `transform.apply_conversion_patterns.dialect_to_llvm "fun"`.

This is dependent on how we want to handle the type converter creation.
In particular the current implementation exhibits the fact that
`transform.apply_conversion_patterns.memref.memref_to_llvm_type_converter` was not rich enough
and did not match the LowerToLLVMOptions.

Keeping those options in sync across all the passes that lower to LLVM is very error prone.
Instead, we should have a single `to_llvm_type_converter`.

Differential Revision: https://reviews.llvm.org/D157553