IEditor: Make duplicatesSupported a value member

src/plugins/android/javaeditor.cpp

src/plugins/android/javaeditor.h

src/plugins/cmakeprojectmanager/cmakeeditor.cpp

src/plugins/cmakeprojectmanager/cmakeeditor.h

src/plugins/coreplugin/editormanager/ieditor.cpp

src/plugins/coreplugin/editormanager/ieditor.h

src/plugins/cppeditor/cppeditor.cpp

src/plugins/cppeditor/cppeditor.h

src/plugins/diffeditor/diffeditor.h

...ugins/genericprojectmanager/genericprojectfileseditor.cpp

...plugins/genericprojectmanager/genericprojectfileseditor.h

src/plugins/glsleditor/glsleditoreditable.cpp

src/plugins/glsleditor/glsleditoreditable.h

src/plugins/pythoneditor/pythoneditor.cpp

src/plugins/pythoneditor/pythoneditor.h

src/plugins/qmakeprojectmanager/profileeditor.cpp

src/plugins/qmakeprojectmanager/profileeditor.h

src/plugins/qmljseditor/qmljseditoreditable.cpp

src/plugins/qmljseditor/qmljseditoreditable.h

src/plugins/texteditor/plaintexteditor.cpp