This PR adds an assert to `CommandReturnObject::{AppendNote,
AppendWarning}` to ensure the diagnostics don't end with a newline,
which is added by the function, or a period, which goes against the
coding standards.
I added a little helper that asserts in assert-enabled builds and trim
the diagnostic otherwise. I know that goes against the notion that
"asserts are preconditions" and therefore you shouldn't handle the case
where they don't hold (something I generally advocate for) but I think
we should prioritize a consistent user experience over purity.
We should do the same thing for `AppendError`, but currently there are
still too many violations that need to be cleaned up and if the compiler
emits non-compliant diagnostics, we may not be able to do this at all.
37a8c71818