[DebugInfo][DAG] Don't reuse debug location on COPY if width changes.

Summary:
This caused incorrect debug information for parameters:
Previously, after a COPY of a parameter that changes the width,
we would emit a DBG_VALUE that continues to be associated to that
parameter, even though it now used a different width.
This made the LiveDebugValues pass assume the parameter value
got clobbered and it stopped tracking the parameter entry
value, leading to incorrect debug information.

Fixes https://bugs.llvm.org/show_bug.cgi?id=39715

Subscribers: aprantl, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80819