[StackColoring] Pre-commit of test case showing a debug invariance bug

Having DBG_VALUE instructions referencing a stack slot while being outside
of the LIFETIME_START/LIFETIME_END markers for that stack slot is perhaps
not always ideal (from a debugging perspective), but it might happen during
codegen that we end up with such situations (e.g. positioning of the
DBG_VALUE instruction for a SDDbgOperand::FRAMEIX at ISel is a bit sloppy
in that context).

This patch adds a test case showing that StackColoring currently isn't
debug invariant, and that the position of DBG_VALUE instructions referencing
the stack slots might impact the decision making regarding stack slot reuse.

Differential Revision: https://reviews.llvm.org/D109757