Apply busy indicator duration change of D22646 to the QQC2 style

Summary:
Match the duration (2 seconds) that was set in D22630.

This style is mainly used by Plasma Mobile, therefore requesting team review from that project as well.

Reviewers: VDG, Plasma:_mobile, ngraham

Reviewed By: VDG, ngraham

Subscribers: ngraham, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D22720