Font zooming should be more visible/accessible

Relevant commit 82e9bc176c4e990e9a01a6182c64663b3a1d605c ( Add font size storage/unified handling in Linguists editors , https://codereview.qt-project.org/#change,74013 ):

By no doing of my own, suddenly the editor font was very small in linguist. Some digging revealed that something goes wrong in the above mentioned change, the font size saved in the settings was 7.5.

My guess is that the font size was initialized to some default in the MessageEditor constructor and then saved in the settings.

IMO, this patch needs improvement:

Instead of the point size, the scaling factor should be saved in the settings and only if !qFuzzyCompare(factor, 1.0).

The setting should be made visible to the user and the user should be able to clear it.

Also, as a long-term Linguist user, I have to say the benefit of the change is questionable.