Summary:
Androidx introduced new Materialcomponents themes, use them instead of
Theme.AppCompat. This also causes AlertDialogs and PreferenceDialogFragments
to be styled correctly

|{F6531506}|{F6531505}|
|Before|After|

(Ok button is disabled if you are wondering)

Test Plan: Apply patch, verify everything still looks as expected

Reviewers: #kde_connect, albertvaka

Reviewed By: #kde_connect, albertvaka

Subscribers: kdeconnect

Tags: #kde_connect

Differential Revision: https://phabricator.kde.org/D18039