Move MinimizableInfoBars from CppEditorDocument to IDocument

Similar to the InfoBar.

The only thing that an editor implementation needs to do is to set a
settings group and the possible info bars in the document constructor.
And later call document->minimizableInfoBars()->setInfoVisible(id,
visible) to manage the state.

Change-Id: I23afb3639b70b1bfccd424579da018280a7fe2cb
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/coreplugin/idocument.h

@@ -35,6 +35,7 @@
 namespace Utils {
 class FilePath;
 class InfoBar;
+class MinimizableInfoBars;
 } // namespace Utils
 
 namespace Core {
@@ -133,6 +134,7 @@ public:
     void setWriteWarning(bool has);
 
     Utils::InfoBar *infoBar();
+    Utils::MinimizableInfoBars *minimizableInfoBars();
 
 signals:
     // For meta data changes: file name, modified state, ...