Simplify wxEventLoopManual pending events processing logic.

Simplify wxEventLoopManual pending events processing logic.

Don't try to process any remaining pending events in ProcessEvents() itself as
this was inconsistent: we only processed low-level toolkit pending events in
the main event loop itself if the loop was exited from a normal event handler
but only processed the wxApp-level pending events if it was exited from a
pending event handler. It also required more code than the new version that
simply processes all the remaining pending events, of both kinds, after the
main event loop termination.

This corrects changes of r71304 and replaces those of r71329.

Closes #14250.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71432 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775