[CodeExtractor] Only rewrite scope of non-inlined variables

When a dbg.value instruction for a variable V is extracted into a new
function, the scope of the underlying variable should be set to the new
function iff V was in the scope of the old function (i.e. it hadn't been
inlined). Prior to this patch, the code extractor would always update
the scope of V.

Differential Revision: https://reviews.llvm.org/D139669