Add new standard KDE tab switching shortcuts (ctrl+pgup/pgdn)

Summary:
BUG: 383603

Add the new KDE standard tab switching shortcuts that were introduced in https://phabricator.kde.org/R237:d85a57645f94d2d087711d7c608a0c5a46ed7ede.

Test Plan: Built and tested with current git master in up-to-date KDE Neon. Expected behavior is seen (default shortcuts have become shift+left/right and cmd+pgup/pgdn).

Reviewers: #kde_applications, #konsole, hindenburg, aacid, ltoscano, pino, dfaure

Reviewed By: dfaure

Subscribers: dfaure, davidedmundson, aacid, #konsole

Tags: #konsole

Differential Revision: https://phabricator.kde.org/D7354