Edit the `findValueInReverseUseDefChain` method to accept `OpOperand`
instead of the `Value` type, This change will make sure that the
populated `visitedOpOperands` argument is fully accurate and contains
the opOperand we have started the reverse chain from.

Note that PointerUnion::{is,get} have been soft deprecated in
PointerUnion.h:

  // FIXME: Replace the uses of is(), get() and dyn_cast() with
  //        isa<T>, cast<T> and the llvm::dyn_cast<T>

I'm not touching PointerUnion::dyn_cast for now because it's a bit
complicated; we could blindly migrate it to dyn_cast_if_present, but
we should probably use dyn_cast when the operand is known to be
non-null.

This change cleans up call sites. Next step is to mark the member
functions deprecated.

See https://mlir.llvm.org/deprecation and
https://discourse.llvm.org/t/preferred-casting-style-going-forward.

For some reason this was missing from STLExtras.

This commit renames 4 pattern rewriter API functions:
* `updateRootInPlace` -> `modifyOpInPlace`
* `startRootUpdate` -> `startOpModification`
* `finalizeRootUpdate` -> `finalizeOpModification`
* `cancelRootUpdate` -> `cancelOpModification`

The term "root" is a misnomer. The root is the op that a rewrite pattern
matches against
(https://mlir.llvm.org/docs/PatternRewriter/#root-operation-name-optional).
A rewriter must be notified of all in-place op modifications, not just
in-place modifications of the root
(https://mlir.llvm.org/docs/PatternRewriter/#pattern-rewriter). The old
function names were confusing and have contributed to various broken
rewrite patterns.

Note: The new function names use the term "modify" instead of "update"
for consistency with the `RewriterBase::Listener` terminology
(`notifyOperationModified`).

`bufferization.materialize_in_destination` should be used instead. Both
ops bufferize to a memcpy. This change also conceptually cleans up the
memref dialect a bit: the memref dialect no longer contains ops that
operate on tensor values.

This revision adds support to
`transform.structured.bufferize_to_allocation` to bufferize
`bufferization.alloc_tensor()` ops.
    
This is useful as a means path to control the bufferization of
`tensor.empty` ops that have bene previously
`bufferization.empty_tensor_to_alloc_tensor`'ed.

This commit allows to omit insertion of the memref.dealloc operation
when linalg.structured.bufferize_to_allocation is run and makes this the
default behavior. This is desirable when the
buffer-deallocation-pipeline is run after bufferization to handle buffer
deallocation.

`bufferize_to_allocation` does not supports ops with regions, unless `bufferize_destination_only` is set. In that case, only the operand is replaced with an allocation and wrapped in a `to_tensor` op. The error checking was too strict.

Differential Revision: https://reviews.llvm.org/D159420