Python: Add DuckTyping::hasUnreliableMro

Primarily used to filter out false positives in cases where our MRO
approximation may be wrong.

Author: tausbn

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowDispatch.qll

@@ -2118,6 +2118,19 @@ module DuckTyping {
    */
   Function getInit(Class cls) { result = invokedFunctionFromClassConstruction(cls, "__init__") }
 
+  /**
+   * Holds if `cls` or any of its superclasses uses multiple inheritance, or
+   * has an unresolved base class. In these cases, our MRO approximation may
+   * resolve to the wrong `__init__`, so we should not flag argument mismatches.
+   */
+  predicate hasUnreliableMro(Class cls) {
+    exists(Class sup | sup = getADirectSuperclass*(cls) |
+      exists(sup.getBase(1))
+      or
+      hasUnresolvedBase(sup)
+    )
+  }
+
   /**
    * Holds if `f` overrides a method in a superclass with the same name.
    */