The presentation compiler API is unclear on this point, but every `askLoadedType` keeps those files in the PC cache, and they get typechecked for each keystroke. Other methods, like `parsedEntered` take a boolean, `keepLoaded`, but that's not the case here.
Our code should be inspected for calls to this method, and make sure we don't increase the list of sources unnecessarily. In fact, any call to `askLoadedType` that is not done on "editor open" should make sure to unload the unit.
- `ScalaSourceFileEditor.reportMatches` does it (seems like the worst offender)
- `ScalaIdeRefactoring.selection` does it too, but maybe it's only loading already loaded files (need to check)