Restore text drag-and-drop in wxSTC broken by Scintilla 2 update.

Drag and drop in wxStyledTextCtrl was broken, apparently since upgrade to
Scintilla 2. Restore it by using the correct wxDrag_XXX constants instead of
boolean values in the code for wxEVT_STC_START_DRAG events generation.

Closes #11709.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65827 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/stc/stc.cpp

@@ -4573,7 +4573,7 @@ wxStyledTextEvent::wxStyledTextEvent(wxEventType commandType, int id)
     m_listType = 0;
     m_x = 0;
     m_y = 0;
-    m_dragAllowMove = false;
+    m_dragAllowMove = wxDrag_CopyOnly;
 #if wxUSE_DRAG_AND_DROP
     m_dragResult = wxDragNone;
 #endif