[mlir][tensor][bufferize] Fix tensor.insert_slice regression

This reverts D132662 (apart from overall cleanups), which introduced a too aggressive optimization for tensor.insert_slice bufferization. Instead, bufferizesToMemoryRead is improved to handle some of these cases. The remaining cases can still bufferize efficiently when running the canonicalizer before the bufferization.

Differential Revision: https://reviews.llvm.org/D138745