CppEditor: Rework showing/switching parse configurations

* Move the combox box for switching the parse configurations out of the
  "Additional Preprocessor Directives" dialog ('#'-button) to make it
  better visible/accessible. Also, decouple the extra preprocessor
  directives from the concrete parse context since this is not anymore
  in same dialog.
* The combo box appears only if multiple parse configurations are
  available for a file.
* The first time multiple parse configurations are detected, an info bar
  is shown that points the user to the combox box. A "Do Not Show Again"
  button is provided.
* Upon selecting an entry, the preferred parse configuration is saved as
  part of the session. The setting can be cleared with the context menu
  entry on the combo box.

Follow-up changes need to ensure that the display name and/or tooltip is
unambiguous, e.g. for qbs and cmake projects.

Change-Id: I9e9773704187291524ad7b605bfdddd83ef5b19d
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/cpptools/cpptools_utils.h

@@ -34,14 +34,29 @@ enum class Language { C, Cxx };
 class ProjectPartInfo {
 public:
     enum Hint {
-        NoHint,
-        IsFallbackMatch,
-        IsAmbiguousMatch
+        NoHint = 0,
+        IsFallbackMatch  = 1 << 0,
+        IsAmbiguousMatch = 1 << 1,
+        IsPreferredMatch = 1 << 2,
+        IsFromProjectMatch = 1 << 3,
+        IsFromDependenciesMatch = 1 << 4,
     };
+    Q_DECLARE_FLAGS(Hints, Hint)
+
+    ProjectPartInfo() = default;
+    ProjectPartInfo(const ProjectPart::Ptr &projectPart,
+                    const QList<ProjectPart::Ptr> &projectParts,
+                    Hints hints)
+        : projectPart(projectPart)
+        , projectParts(projectParts)
+        , hints(hints)
+    {
+    }
 
 public:
     ProjectPart::Ptr projectPart;
-    Hint hint;
+    QList<ProjectPart::Ptr> projectParts; // The one above as first plus alternatives.
+    Hints hints = NoHint;
 };
 
 } // namespace CppTools