[CodeExtractor] Transfer debug info to extracted function

After extracting, fix up debug info in both the old and new functions by

1) Pointing line locations and debug intrinsics to the new subprogram
   scope, and

2) Deleting intrinsics which point to values outside of the new
   function.

Depends on https://reviews.llvm.org/D72795.

Testing: check-llvm, check-clang, a build of LNT in the `-Os -g` config
with "-mllvm -hot-cold-split=1" set, and end-to-end debugging of a toy
program which undergoes splitting to verify that lldb can find
variables, single step, etc. in extracted code.

rdar://45507940

Differential Revision: https://reviews.llvm.org/D72801