[RemoveDIs][DebugInfo] Perform some pre-turn-on test maintenence (#80885)

As we'll hopefully move away from using intrinsics for debug-info
shortly, this commit stabilizes a few tests to avoid spurious changes in
the process. Briefly, there are differences in output when we don't use
intrinsics that we're going to suppress in case we have to revert, these
are:
* The attributor test gets different attributes for the dbg.value
intrinsic because it's not present during optimisation. This has no
functional effect and there's no need to test for it.
* The Scalarizer test exposes a "debug-info affects codegen" problem,
but fixing it is fiddly (updating 20 IRBuilder object calls). Pin this
test to not change with RemoveDIs, we can relax it later and get the
correct behaviour.
* DIDefaultTemplateParam.ll tests for explicit metadata node numbers
which is generally bad. Add explicit node-number capturing CHECK lines.