Core: Make IEditor::id a value member and adjust users

src/plugins/android/androidmanifesteditor.cpp

src/plugins/android/androidmanifesteditor.h

src/plugins/android/javaeditor.cpp

src/plugins/android/javaeditor.h

src/plugins/bineditor/bineditorplugin.cpp

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.cpp

src/plugins/diffeditor/diffeditor.h

src/plugins/diffeditor/sidebysidediffeditorwidget.cpp

...ugins/genericprojectmanager/genericprojectfileseditor.cpp

...plugins/genericprojectmanager/genericprojectfileseditor.h

src/plugins/glsleditor/glsleditor.cpp

src/plugins/glsleditor/glsleditoreditable.cpp

src/plugins/glsleditor/glsleditoreditable.h

src/plugins/imageviewer/imageviewer.cpp