[DebugInfo][InstrRef][NFC] Test changes: DBG_VALUE to DBG_INSTR_REF

This patch contains a bunch of replacements of:

    DBG_VALUE $somereg

with,

    SOMEINST debug-instr-number1
    DBG_INSTR_REF 1, 0, ...

It's mostly SelectionDAG tests that are making sure that the variable
location assignment is placed in the correct position in the instructions.

To avoid a loss in test coverage of SelectionDAG, which is used by a lot
of different backends, all these tests now have two modes and sets of RUN
lines, one for DBG_VALUE mode, the other for instruction referencing.

Differential Revision: https://reviews.llvm.org/D114258