Allow Ctrl+Wheel to zoom in/out on the target text

Summary:
Allow Ctrl+Wheel to zoom in and out of the target text (change its font size) when the wheel navigation is disabled.
This makes the target field more consistent with the source field.
By default the QTextEdit Qt component allows Ctrl+Wheel zooming only for read only fields.

https://bugs.kde.org/show_bug.cgi?id=375251

Reviewers: #localization, aacid, ltoscano, shaforostoff, mlaurent

Reviewed By: #localization, aacid

Subscribers: safaalfulaij

Tags: #localization

Differential Revision: https://phabricator.kde.org/D14151