Invokes a setter and returns a mirror on the result.
The setter may be either the implicit setter for a non-final field or a user-defined setter method.
Let o be the object reflected by this mirror,
let f be the simple name of the getter denoted by
and let a be the object bound to
Then this method will perform the setter invocation o.f = a in a scope that has access to the private members of o (if o is a class or library) or the private members of the class of o (otherwise).
If the invocation returns a result r, this method returns the result of
If the invocation causes a compilation error, the effect is the same as if a non-reflective compilation error had been encountered.
If the invocation throws an exception e (that it does not catch) this method throws e.
/* TODO(turnidge): Handle ambiguous names.*/ InstanceMirror setField(Symbol fieldName, Object value);