[DebugInfo] Fix jump threading failing to update cloned dbg.values

This is a patch to fix duplicated dbg.values in the JumpThreading pass not
pointing towards their local value, and instead towards the variable in the
original block.
JumpThreadingPass::cloneInstructions is the changed function to target metadata
as well as normal cloned values.

Reviewed By: jmorse, StephenTozer

Differential Revision: https://reviews.llvm.org/D140006