[mlir][memref][transform] Add vector_to_llvm conversion patterns

These patterns are exposed via a new "apply_conversion_patterns" op.

Also provide a new type converter that converts from memref to LLVM types. Conversion patterns that lower to LLVM are special: they require an `LLVMTypeConverter`; a normal `TypeConverter` is not enough. This revision also adds a new interface method to pattern descriptor ops to verify that the default type converter of the enclosing "apply_conversion_patterns" op is compatible with the set of patterns. At the moment, a simple `StringRef` is used. This can evolve to a richer type in the future if needed.

Differential Revision: https://reviews.llvm.org/D157369