Bug 792470 - Some filters e.g. "Levels" are not added to "Repeat last" history
The four remaining "classic" color tools (Brightness-Contrast, Curves, Levels and Threshold) are in fact just special UIs for otherwise completely normal filter ops. Add normal filter actions for them and invoke them like all other filters, which makes them show up in the filter history automatically. The only small hack needed is to special case them in gimp_gegl_procedure_execute_async() so the right tools are created instead of the default GimpOperationTool. Also, blacklist the automatically generated tools actions from action search and the shortcut editor.
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