Touch gestures: add right mouse click (tap and hold) command (#10065)
* Global commands: added a gesture to perform right click on touch screens. re #3886.
* Oops - fix indentation.
* Global Commands: touch right click - ignore invisible or offscreen objects, as well as if any of the object coordinates is negative. re #3886.
In some cases, objects may appear invisible until focus moves to it. This is noticeable on www.webaim.org's skip to content anchor.
Also don't bother clicking when the minimum of the coordinates is negative.
Also modified script doc for touch_rightClick (all suggested by jamie@nvaccess.org).
* Remove blank line.
* User guide: document tap and hold for right mouse click on touch devices, reword introductory text for mouse commands table. Re #3886
* Touch right mouse click/Python 3: coordinates should be integers, not float. re #3886.
* Touch mouse command: lint fixes. Re #3886.
Lint fixes include spaces around operators, dictionary key/value assignment, and three noqa comments.