Implement the Starlark index expression assignment operation (#497)

* CSL3-2071 CSL3-2108 - Case Insensitive headers test

* Failing test demonstrating issue with assignment of d["key"] = "one" throwing an exception.

The error message is: Error: can only assign an element in a dictionary or a list, not in a 'MutableStruct'. Let's make the tests pass!

* We introduce StarlarkSetIndexable to allow setIndex, similar to
StarlarkIndexable.

We follow the exact same interface and modifications for
StarlarkIndexable and update the error message to signify that we now
support setIndex on dictionaries, lists, and any implementation of
StarlarkSetIndexable. We also support the equivalent
StarlarkIndexable.Threaded interface for StarlarkSetIndexable,
similary called StarlarkSetIndexable.Threaded.

* Update tests to support usage pattern

* Update LarkyIndexable to support __setitem__ and implement the new StarlarkSetIndexable(.Threaded) interface

* And now, we do not need StarlarkMapping any longer since we can fulfill the exact same interface with LarkyMapping. Delete StarlarkMapping and move the functionality to LarkyMapping

* Fix incorrect test syntax -- there is no .size() in Python, only len(dict) for cardinality checks

* we do not have a base itemview class in larky, so we cannot compare classes to primitives in larky (as we would do in python). as a result, we have to return a raw list on the view instead of an actual view

* We make the final modification to get the test to pass!

---------

Co-authored-by: Sasha Kochniev <[email protected]>

larky/src/main/java/com/verygood/security/larky/modules/types/LarkyIndexable.java

@@ -2,16 +2,22 @@
 
 import com.google.common.collect.ImmutableList;
 
+import com.verygood.security.larky.parser.StarlarkUtil;
+
 import net.starlark.java.eval.EvalException;
 import net.starlark.java.eval.Starlark;
 import net.starlark.java.eval.StarlarkCallable;
-import net.starlark.java.eval.StarlarkIndexable;
 import net.starlark.java.eval.StarlarkSemantics;
+import net.starlark.java.eval.StarlarkSetIndexable;
 import net.starlark.java.eval.StarlarkThread;
 import net.starlark.java.syntax.TokenKind;
 
 
-public interface LarkyIndexable extends LarkyObject, StarlarkIndexable.Threaded {
+public interface LarkyIndexable extends LarkyObject, StarlarkSetIndexable.Threaded {
+
+  default Object get__setitem__() {
+    return getField(PyProtocols.__SETITEM__);
+  }
 
   default Object get__getitem__() {
     return getField(PyProtocols.__GETITEM__);
@@ -22,6 +28,17 @@ default Object get__contains__() {
     return getField(PyProtocols.__CONTAINS__);
   }
 
+  @Override
+  default void setIndex(StarlarkThread starlarkThread, StarlarkSemantics semantics, Object key, Object value) throws EvalException {
+    final Object __setitem__ = get__setitem__();
+    if(__setitem__ != null && StarlarkUtil.isCallable(__setitem__)) {
+      Starlark.checkHashable(key);
+      this.invoke(starlarkThread, __setitem__, ImmutableList.of(key, value), EMPTY_KWARGS);
+      return;
+    }
+    throw Starlark.errorf("TypeError: '%s' object does not support item assignment", typeName());
+  }
+
   @Override
   default Object getIndex(StarlarkThread starlarkThread, StarlarkSemantics semantics, Object key) throws EvalException {
     // The __getitem__ magic method is usually used for list indexing, dictionary lookup, or