- Moved wxApp::SendIdleEvents and wxApp::ProcessIdle into common code.

- Moved wxApp::SendIdleEvents and wxApp::ProcessIdle into common code.
- wxWindow::OnInternalIdle is now used in all ports, and ensures that
  user OnIdle events do not interfere with crucial internal processing.
- wxWindow::UpdateWindowUI is now a documented function that
  sends wxUpdateUIEvents, and can be overridden. It has a helper function
  DoUpdateWindowUI for taking appropriate wxUpdateUIEvent action.
- Added functions to wxUpdateUIEvent: Set/GetMode, Set/GetUpdateInterval,
  CanUpdate, to assist with optimising update event frequency.
- Added functions to wxIdleEvent: Set/GetMode, CanSend, to
  determine whether a window should receive idle events.
- Added wxWS_EX_PROCESS_IDLE, wxWS_EX_PROCESS_UI_UPDATES window
  styles for use with conservative idle and update event modes.
- wxMSW and wxGTK now send menu update events only when a menu is
  about to be used.
- Added WM_INITMENU processing instead of WM_ENTERMENULOOP, or
  accelerators don't always get called since menu items may still
  be disabled.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@21789 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775