[SplitEdge] Add new parameter to SplitEdge to name the newly created basic block

Summary:
Currently SplitEdge does not support passing in parameter which allows you to
name the newly created BasicBlock.

This patch updates the function such that the name of the block can be passed
in, if users of this utility decide to do so.

Reviewed By: Whitney, bmahjour, asbirlea, jamieschmeiser

Differential Revision: https://reviews.llvm.org/D94176