Reapply: [NFC] Move getDebugValueLoc from static in Local.cpp to DebugInfo.h

Reverted in b22d80dc.

Move getDebugValueLoc so that it can be accessed from DebugInfo.h for the
Assignment Tracking patch stack and remove redundant parameter Src.

Reviewed By: jryans

Differential Revision: https://reviews.llvm.org/D132357