[mlir][bufferize] Improve resolveConflicts for ExtractSliceOp

It is sometimes better to make a copy of the OpResult instead of making a copy of the OpOperand. E.g., when bufferizing tensor.extract_slice.

This implementation will eventually make parts of extract_slice's `bufferize` implementation obsolete (and simplify it). It will only need to handle in-place OpOperands.

Differential Revision: https://reviews.llvm.org/D126819