create Variant Dictionary method map() similar to Variant Array method map()

[Efimero]

I believe it would be very useful to have a Dictionary::map() method in GDScript similar to what Array has.
Array::map()

It would work in a similar fashion, but the lambda provided would have two parameters, for the key and the value, and would return a new value for that key. This would enable better, more readable code in cases where you want to (immutably) alter a dictionary preserving the keys.

For example:

func num_from_range(k: StringName, v: Array) -> int:
  return randi_range(v[0], v[1])

func read_template(d: Dictionary) -> Dictionary:
  return d.map(num_from_range)

read_template({&"ruff": [3, 7], &"woof": [40, 80], &"mlem": [200, 789]})
# ==> {&"ruff": 4, &"woof": 69, &"mlem": 420}

[Efimero]

With some help from a friend, we figured this might be the code that would be added to Dictionary.cpp

Variant Dictionary::map(const Callable &p_callable) const {
        Dictionary n;

        for (const KeyValue<Variant, Variant> &E : _p->variant_map) {
            const Variant **argptrs = (const Variant **)alloca(2 * sizeof(Variant *));
            argptrs[0] = &E.key;
            argptrs[1] = &E.value;
            Variant result;
            Callable::CallError ce;
            p_callable.call(argptrs, 2, result, ce);
            if (ce.error != Callable::CallError::CALL_OK) {
                ERR_FAIL_V_MSG(Array(), "Error calling method from 'map': " + Variant::get_callable_error_text(p_callable, argptrs, 2, ce));
            }
            n[E.key] = result;
        }

        return n;
}