[mlir][bufferization][NFC] Move more unknown type conversion logic into BufferizationOptions

The `unknownTypeConversion` bufferization option (enum) is now a type converter function option. Some logic of `getMemRefType` is now handled by that function.

This change makes type conversion more controllable. Previously, there were only two options when generating memref types for non-bufferizable ops: Static identity layout or fully dynamic layout. With this change, users of One-Shot Bufferize can provide a function with custom logic.

Differential Revision: https://reviews.llvm.org/D129273