[SelectionDAG] Add OPC_MoveSibling (#73643)

There are a lot of operations to move current node to parent and
then move to another child.

So `OPC_MoveSibling` and its space-optimized forms are added to do
this "move to sibling" operations.

These new operations will be generated when optimizing matcher in
`ContractNodes`. Currently `MoveParent+MoveChild` will be optimized
to `MoveSibling` and sequences `MoveParent+RecordChild+MoveChild`
will be transformed into `MoveSibling+RecordNode`.

Overall this reduces the llc binary size with all in-tree targets by
about 30K.