PY-19127 Fixed: __prepare__ magic function not hightlights

Add __prepare__ to py3 builtin methods

python/psi-api/src/com/jetbrains/python/PyNames.java

@@ -392,6 +392,7 @@ public class PyNames {
     .put("__bool__", _only_self_descr)
     .put("__bytes__", _only_self_descr)
     .put("__format__", new BuiltinDescription("(self, format_spec)"))
+    .put("__prepare__", new BuiltinDescription("(metacls, name, bases)"))
     .put("__round__", new BuiltinDescription("(self, n=None)"))
     .put(DUNDER_NEXT, _only_self_descr)
     .build();

python/testData/completion/dunderPrepare.after.py

@@ -0,0 +1,2 @@
+class C:
+    def __prepare__(metacls, name, bases):

python/testData/completion/dunderPrepare.py

@@ -0,0 +1,2 @@
+class C:
+    def __prep<caret>

python/testSrc/com/jetbrains/python/Py3CompletionTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2013 JetBrains s.r.o.
+ * Copyright 2000-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -160,6 +160,11 @@ public class Py3CompletionTest extends PyTestCase {
     runWithLanguageLevel(LanguageLevel.PYTHON35, () -> doTest());
   }
 
+  // PY-17828
+  public void testDunderPrepare() {
+    runWithLanguageLevel(LanguageLevel.PYTHON30, this::doTest);
+  }
+
   @Override
   protected String getTestDataPath() {
     return super.getTestDataPath() + "/completion";