CppTools: Use cursor range for better outline navigation

Clang provides cursor range for each declaration in
symbol outline. Use that information to search for
more accurate correspondence between a cursor position
in editor and an entry in symbol outline.

For example skip indexes with not matching ranges to
prevent pure declarations from automatically become
parents of everything coming after them.

Change-Id: I0ef95c26772050cd6655e830288c46118aba38bb
Reviewed-by: Nikolai Kosjar <nikolai.kosjar@qt.io>

src/plugins/cpptools/abstractoverviewmodel.h

@@ -32,6 +32,8 @@
 
 #include <QSharedPointer>
 
+#include <utility>
+
 namespace CPlusPlus { class Document; }
 
 namespace Utils {
@@ -91,6 +93,9 @@ public:
     virtual Utils::Link linkFromIndex(const QModelIndex &) const = 0;
     virtual Utils::LineColumn lineColumnFromIndex(const QModelIndex &) const = 0;
 
+    using Range = std::pair<Utils::LineColumn, Utils::LineColumn>;
+    virtual Range rangeFromIndex(const QModelIndex &) const = 0;
+
 signals:
     void needsUpdate();
 };