This PR significantly improves the test coverage of the language server,
providing at least a single basic test for every request that is used by
the client. It also implements infrastructure for testing all of these
requests, e.g. the ability to run interactive tests in a project context
and refactors the interactive test runner to be more maintainable.
Finally, it also fixes a small bug with the recently implemented unknown
identifier code actions for auto-implicits (#10442) that was discovered
in testing, where the "import all unambiguous unknown identifiers" code
action didn't work correctly on auto-implicit identifiers.
When the elaborator doesn't provide us with any `CompletionInfo`, we
currently provide no completions whatsoever. But in many cases, we can
still provide some helpful identifier completions without elaborator
information. This PR adds a fallback mode for this situation.
There is more potential here, but this should be a good start.
In principle, this issue alleviates #5172 (since we now provide
completions in these contexts). I'll leave it up to an elaboration
maintainer whether we also want to ensure that the completion infos are
provided correctly in these cases.
