This is the last main block of bringing the new plugin features to other hosting apps (but I'll still follow up with one or more cleanup patches for the MainWindow interface).
As was to be expected, this one was a little more involved. Some notes:
- Added two additional functions to ktexteditor_utils.cpp, neither would seem mandatory to implement in a hosting application.
- Construction of the DiagnosticsView tries to follow the existing logic in kate, but in other hosting apps, it will be constructed, lazily, as a side-effect of the first DiagnosticsProvider registering.
- One missing bit so far is reading / writing the diagnostic sessionConfig outside of kate.
- Handling the Esc key looks like a candidate for factoring out, entirely. For now, I copied a solution from kateexternaltoolsview.