Android: pinch zoom to enlarge fonts

Idea: add pinch zoom to enlarge fonts which can be difficult to read (password/login) in some situations, hence a zoom in/out would be handy

No files or tests are named. Start by locating the Android password and login screens and checking existing text-size and gesture handling; clarify which screens and zoom limits are in scope. Done should mean the intended fonts can be enlarged and reduced with pinch gestures without disrupting secure entry.

Written by the indexing model from the issue text.