[CodeGenPrepare] The instruction to be sunk should be inserted before its user in a block

In current implementation, the instruction to be sunk will be inserted before the target instruction without considering the def-use tree,
which may case Instruction does not dominate all uses error. We need to choose a suitable location to insert according to the use chain

Reviewed By: dmgreen

Differential Revision: https://reviews.llvm.org/D107262