Ensure that Enter key presses are never stolen from wxButton in wxMSW.

This commit fixes the following bug: when an in-place editor control containing
an embedded button was used in wxDataViewCtrl, pressing Enter on the button
would close the editor, accepting changes, instead as (generic) wxDataViewCtrl
intercepts WXK_RETURN in its EVT_CHAR_HOOK handler. To prevent this from
happening, wxButton now handles EVT_CHAR_HOOK itself and never lets the parent
window intercept it if it's for WXK_RETURN. To ensure that normal
wxEVT_KEY_DOWN and wxEVT_CHAR are still generated in this case, wxButton
handler calls the new wxKeyEvent::DoAllowNextEvent() method that was added to
allow suppressing EVT_CHAR_HOOK only, without affecting the subsequent events.
DoAllowNextEvent() is currently only used in wxMSW but support for it was also
added to wxGTK and (both) wxOSX ports.

See #9102.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69984 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/event.h

@@ -1707,6 +1707,15 @@ public:
     // Get Y position
     wxCoord GetY() const { return m_y; }
 
+    // Can be called from wxEVT_CHAR_HOOK handler to allow generation of normal
+    // key events even though the event had been handled (by default they would
+    // not be generated in this case).
+    void DoAllowNextEvent() { m_allowNext = true; }
+
+    // Return the value of the "allow next" flag, for internal use only.
+    bool IsNextEventAllowed() const { return m_allowNext; }
+
+
     virtual wxEvent *Clone() const { return new wxKeyEvent(*this); }
     virtual wxEventCategory GetEventCategory() const { return wxEVT_CATEGORY_USER_INPUT; }
 
@@ -1750,6 +1759,8 @@ private:
     {
         if ( m_eventType == wxEVT_CHAR_HOOK )
             m_propagationLevel = wxEVENT_PROPAGATE_MAX;
+
+        m_allowNext = false;
     }
 
     // Copy only the event data present in this class, this is used by
@@ -1768,6 +1779,11 @@ private:
 #endif
     }
 
+    // If this flag is true, the normal key events should still be generated
+    // even if wxEVT_CHAR_HOOK had been handled. By default it is false as
+    // handling wxEVT_CHAR_HOOK suppresses all the subsequent events.
+    bool m_allowNext;
+
     DECLARE_DYNAMIC_CLASS(wxKeyEvent)
 };