Properly Log Errors

[InsertCreativityHere]

Currently, whenever we encounter an error (Result::Err I'm talking about), we usually just ignore it by calling ok(), then skipping whatever we were about to do.

It would be better to properly report any actual errors back to the language client, instead of silently hiding them.

[ReeceHumphreys]

Some of this errors should just be emitted to the Slice trace while others emitted to the user in the form of a popup like how 0e69963 does for Diagnostics without spans.