This will make it easier for me with a few further refactors to make the
ownership verifier testing mode emit per function error numbers instead of the
global error number that it is emitting now.
The reason why this is necessary is that today, the verification by
-sil-verify-all causes the errors to be emitted. That verification is done on a
per value level, rather than a per function level, so it is hard to get per
function error numbers without doing unprincipled things like propagating around
state saying what the current function being verified is.
This pass instead will let me make the error counter be per ErrorBuilder which
are created per function.
One thing to be aware of is that this /will/ cause SILValue::verifyOwnership to
not emit any output when the testing flag is enabled. This is to ensure I only
do not get duplicate textual error messages from the SILVerifier.
