IDE Fail safe it there is no direct errors in current document but fail in non-open imported ones

Related to https://github.com/microsoft/cadl/issues/1440 where we might not be running later validation because of an error in a previous step. This is quite problematic in the IDE where the error in the previous step might be in another unopened file and then this cause all the validation in the current file to not run.

Maybe we can have the ide show something like:
- if there is errors but none if any of the opened files then show a "External error in that file preventing this from building"