Let's make use of a newly added "disable for performance" flag to
allow solver to consider overload choices where the only issue is
missing one or more labels - this makes it for a much better
diagnostic experience without any performance impact for valid code.
There's no need to instantiate archetypes in the generic environment
of the declaration being opened.
A couple of diagnostics changed. They were already misleading, and the
new diagnostics, while different, are not any more misleading than
before.
