Revert "Add dropdown dialog implementation" and followups
This reverts commit 535b4b4a and its followups.
That commit was a workaround for KWin bug #452967, which was fixed in KWin 5.25.5 released on 2022-09-06. The workaround is now entirely unnecessary, so switch back to the built-in QtWebEngine/Chromium dropdowns.
There are several reasons why I would like to see the workaround gone:
- It is no longer necessary, so this is extra code that does not need to be maintained anymore. (E.g., porting that dropdown implementation from OverlaySheet to Dialog was entirely unnecessary work.)
- It introduced GPL-3.0-only code, whereas the rest of the code is both backwards-compatible with the GPLv2 and forwards-compatible with future versions of the GPL (at least if and when approved by KDE e.V., though most files even have a blanket "or later" clause).
- It is less reliable than the built-in QtWebEngine/Chromium dropdowns. I have had those custom dropdowns behave strangely on the first touch, selecting a wrong item, and only touching it again made them work properly. They also do not scale for lists with many items in them.