CppEditor: Trigger AddIncludeForUndefinedIdentifier on qualified name base

Now there is no need to position the cursor on "C" of "Namespace::C" to
trigger the quick fix. It will already trigger if the cursor is
somewhere within the name.

Change-Id: Ic99325f95b5cf5551fc74b55606c402461849fb0
Reviewed-by: Christian Stenger <christian.stenger@digia.com>