[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.

Test Plan:
Ensure no loss of functionality, style, or bugs from the port of QQC1 to QQC2.

Reviewers: Plasma, VDG, davidedmundson, filipf

Reviewed By: Plasma, VDG, davidedmundson, filipf

Subscribers: ndavis, GB_2, ngraham, filipf, davidedmundson, plasma-devel

Tags: Plasma

Maniphest Tasks: T10958

Differential Revision: https://phabricator.kde.org/D21815