Improved error reporting

[lextm]

Scenario: When a Sphinx project is being edited, the build fails and succeeds often (especially when conf.py is being changed).

Problem: The current version raises too many error notifications. Besides, "see output window for details" is ambiguous, as some users might not know it is "Esbonio Language Server" channel under OUTPUT panel that they should open and read.

Solution: Removed the error notifications. Instead, automatically open the channel when errors occur.

[alcarney]

I'm not a fan of this solution, only because any client that is not VSCode will now fail silently.
Perhaps the error could be converted into a diagnostic instead?

[lextm]

I added a commit which monitors initialization errors (such as typing something random in conf.py to trigger a config error) and generates error diagnostics from them. However, such diagnostics are not very visible to users (they might simply ignore them). So to me that's not a very convenient way either.

[alcarney]

I agree it's not perfect, but it's probably better than nothing... could update these test cases to look for the diagnostic instead?

[lextm]

Sure. I will check how to update the test cases.

[alcarney]

Thanks for this, the changes have been incorporated into #352