Qt cmake plugin targets resolve each plugin .so via <sysroot>/plugins (the
_IMPORT_PREFIX is computed from the cmake files under <sysroot>/lib/cmake, i.e.
the sysroot root, not <sysroot>/usr), but cmake --install --prefix .../usr puts
plugins at usr/plugins. qtbase already works around this by staging plugins to
BOTH usr/plugins and plugins (recipe.toml ~L739); qtwayland/qtsvg/qtdeclarative
did not, so their plugins (wayland decorations, svg imageformats/iconengines,
qmltooling) were unreachable at <sysroot>/plugins and any Qt6Gui/Qt6Qml consumer
failed: imported target references "<sysroot>/plugins/.../foo.so" but this file
does not exist. This blocked kf6-kwindowsystem (sddm dep) on the Adwaita
decoration plugin. Add a shared redbear_qt_dual_stage_plugins helper and call it
after install in all three. (Note qml already resolves via the qml symlink since
qtbase does not dual-stage qml, so <sysroot>/qml is a symlink not a real dir.)
vasilito
44c054e37d