Move QtWebengine to the runtime

This is a core Qt module, building it as a baseapp with a separate prefix causes a bunch of incompatibility issues.

See

!202 (closed)

https://github.com/flathub/flathub/pull/5433#issuecomment-2245449036

The worst part is that as QtWebengine relies on private Qt ABI, patch version mismatches between runtime core Qt and QtWebengine baseapp cause apps to crash

See https://github.com/flathub/org.kde.arianna/issues/58

To solve the above every time runtime Qt changes the version we have to rebuild QtWebengine baseapp and any baseapp or application dependent on it. Currently, that is Pyside6 baseapp and PyQt baseapp.

This rebuild has to be done manually by someone after someone notices things crashing. This was discussed previously https://github.com/flathub/flathub/issues/1453

There are 22 org.kde. apps using the baseapp:

org.kde.amarok
org.kde.kmymoney
org.kde.cantor
org.kde.digikam
org.kde.kdevelop
org.kde.akregator
org.kde.labplot2
org.kde.kgeotag
org.kde.kphotoalbum
org.kde.arianna
org.kde.kalgebra
org.kde.ghostwriter
org.kde.skanpage
org.kde.tokodon
org.kde.angelfish
org.kde.kontact
org.kde.falkon
org.kde.parley
org.kde.marble
org.kde.kimagemapeditor
org.kde.tellico
org.kde.skrooge

Like the rest of the Qt modules, it should be maintained as part of the runtime.