[SCEVExpander] Use IRBuilderCallbackInserter to call rememberInstruction.
Currently there are plenty of instructions that SCEVExpander creates but
does not track as created. IRBuilder allows specifying a callback
whenever an instruction is inserted. Use this to call
rememberInstruction automatically for each created instruction.
There are still a few rememberInstruction calls remaining, because in
some cases Inst::Create functions are used to construct instructions.
Reviewers: mkazantsev, reames, sanjoy.google, lebedev.ri
Reviewed By: lebedev.ri
Differential Revision: https://reviews.llvm.org/D84326