* Makefile.am: Add new backend.
* configure.ac: Configure desktop file for Qt5 backend.
* doc/pinentry.texi: Add Qt6 backend to docs.
* m4/qt6.m4: New.
* qt/Makefile.am: Use Qt6 instead of Qt5.
* qt/capslock.cpp, qt/capslock_p.h, qt/capslock_unix.cpp:
	Port capslock detection from KWayland to KGuiAddons.
* qt/pinentryconfirm.cpp: Adapt to changed function signature.
* qt5/*: Copy from qt/ and rename.