JsInterpreter: ValidateAndApplyPropertyDescriptor, push down type cast
JsInterpreter: ValidateAndApplyPropertyDescriptor, push down type cast

This function takes an object and a property name xor undefined
for both. We had string_of_value casts when the property name could have
been undefined.

jscert/jsexplain,jscert/jsexplain,jscert/jsexplain,jscert/jsexplain,jscert/jsexplain