Clang: Adapt priorities for the same method/constructor overloads

CXXMethod and CXXConstructor may have different priorities
depending ony their origin and attributes. To keep them together
in the sorted list we adapt their priorities to have the same
value if their names match.
To continue keeping ClassCompletion before ConstructorCompletion
change the order of the completion kinds for the sort purposes.

Change-Id: I36efe5d5dbaa77d604a54b1dafe07d67f44db4c9
Reviewed-by: Marco Bubke <marco.bubke@qt.io>

src/plugins/clangcodemodel/clangcompletionassistprocessor.cpp

@@ -113,8 +113,7 @@ static bool isTheSameFunctionOverload(const CodeCompletion &completion,
                                       const QString &name,
                                       ClangAssistProposalItem *lastItem)
 {
-    return completion.hasParameters
-            && completion.completionKind == lastItem->firstCodeCompletion().completionKind
+    return completion.completionKind == lastItem->firstCodeCompletion().completionKind
             && lastItem->text() == name;
 }