[mlir][cf-sink] Accept a callback for sinking operations

(This was a TODO from the initial patch).

The control-flow sink utility accepts a callback that is used to sink an operation into a region.
The `moveIntoRegion` is called on the same operation and region that return true for `shouldMoveIntoRegion`.
The callback must preserve the dominance of the operation within the region. In the default control-flow
sink implementation, this is moving the operation to the start of the entry block.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D122445