[sddm-theme] Start moving from QQC1 to QQC2
Summary: Components that used QQC1 in sddm-theme/ (excluding the symlinked components folder) have been changed to use QQC2.
Ensure no loss of functionality, style, or bugs from the port of QQC1 to QQC2.
Subscribers: ndavis, GB_2, ngraham, filipf, davidedmundson, plasma-devel
Maniphest Tasks: T10958
Differential Revision: https://phabricator.kde.org/D21815