This makes buttons with short texts such as "OK" or "Close"
easier to click, especially on a touchscreen.
This is exposed to projects via `buttons_min_width` and `buttons_min_height`
theme items in AcceptDialog (and therefore ConfirmationDialog and FileDialog),
with the default values being 0 to preserve compatibility with existing projects.
`AcceptDialog`, `Popup` and `PopupMenu` no longer subscribe to
"window_input" signal, because that is only sent if it is not an
internal signal.
Instead they receive events in `_input_from_window`. They ensure that
the event is also propagated to their super-function, just like
previously the signals would be treated.
Fix, that a non-exclusive AcceptDialog with `close_on_escape == true`
gets closed, when the parent window of the parent window receives focus.
There is no need to rely on the focus of the parent visible window.
Instead check if the AcceptDialog loses focus.
As opposed to hardcoding the escape key. Also removed such hardcoding in a few other places as well as a hardcoded enter key in one of the affected input fields.