Summary:
Use androidx version of AlertDialog to get properly styled AlertDialog buttons
Use PreferenceManager context to style Device Name AlertDialog

|{F6551907}|{F6551908}|
|Before|After|

Test Plan: Apply patch and verify that AlertDialogs have properly styled buttons

Reviewers: #kde_connect, albertvaka

Reviewed By: #kde_connect, albertvaka

Subscribers: albertvaka, kdeconnect

Tags: #kde_connect

Differential Revision: https://phabricator.kde.org/D18298