[mlir][bufferization] Add optional `copy` operand to AllocTensorOp

If `copy` is specified, the newly allocated buffer is initialized with the given contents. Also add an optional `escape` attribute to indicate whether the buffer of the tensor may be returned from the parent block (aka. "escape") after bufferization.

This change is in preparation of connecting One-Shot Bufferize to the sparse compiler.

Differential Revision: https://reviews.llvm.org/D126570