The text of an action is used as the tooltip and iconText unless those
are explicitly set, and only then does an '&' mnemonic get stripped.
An '&' in the text will generate mnemonic shortcuts in some UI controls,
such as menubars, menus, or buttons. Document that in the text property,
and add a see-also from the constructor to the relevant properties.
As a drive-by, reduce the usage of "widget" in the documentation.
QAction now lives in QtGui and can be used by both widget and Qt Quick
UIs.
Fixes: QTBUG-109060
Fixes: QTBUG-109061
Pick-to: 6.4 6.2
Change-Id: I5e7c2a01b8029f519d7050187e486b667d3cd52b
Reviewed-by: Paul Wicking <paul.wicking@qt.io>