This breaks existing unit tests using wxUIActionSimulator that do things
similar to
wxUIActionSimulator sim;
sim.Char('o', wxMOD_CMD);
wxTEST_DIALOG(wxYield(), ... expected "Open" dialog ...);
because the expected dialog would be shown from inside Char(), unlike
with the wxMSW implementation and GTK until the changes of 59ad9f46e6
(Make wxUIActionSimulator works more reliably on GTK/X11, 2020-05-07).
To still make sure there is a delay after the event, sleep, if
necessary, before simulating the next event: this is still enough for wx
test suite to pass, but allows the code like above to work with both
wxMSW and wxGTK.
In fact, doing it like this makes the code simpler and removes the need
to distinguish between press and release events or maintaining the
number of currently simulated-as-depressed buttons or keys, so it also
simplifies things as a side effect.
Also add some comments and rename Default_Delay constant to a more
accurately named MIN_DELAY_BETWEEN_EVENTS.
Closes https://github.com/wxWidgets/wxWidgets/pull/2318
cf01fe536d