Aggregation/Utils/ExtensionSystem: Make member functions const/static

readability-make-member-function-const finds lots of member functions
that could be made const. This change just picks getter functions that
really should be const.

readability-convert-member-functions-to-static finds non-static member
functions which do not access this. This change turns most of them
into static ones, but leaves some non static to keep the class API
consistent.

readability-static-accessed-through-instance fixes the places where
the originally non-static, now static functions were called through
instance.

Change-Id: I8cf16c01f7988a7c9d073b5f8ede6a9706b94fb0
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/libs/utils/macroexpander.cpp

@@ -82,7 +82,7 @@ public:
         return this == globalMacroExpander()->d ? false : globalMacroExpander()->d->resolveMacro(name, ret, seen);
     }
 
-    QString value(const QByteArray &variable, bool *found)
+    QString value(const QByteArray &variable, bool *found) const
     {
         MacroExpander::StringFunction sf = m_map.value(variable);
         if (sf) {