Cast to class or interface

Describe the bug
In PXT 4.4, cast to class or interface is not supported.

In PXT 5.5, no error is displayed on the JavaScript editor but the code does not run.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://makecode.microbit.org/beta
2. Switch to JavaScript
3. Paste the code below to the editor

interface Length {
    length: number;
}
function showLength(x: Length) {
    basic.showNumber(x.length);
}
showLength([]);
showLength("X");

4. See error

Expected behavior
Either the cast is disallowed with error or it works successfully.

Start at the JavaScript editor in the PXT micro:bit beta and reproduce the issue with the provided Length interface, showLength function, and calls using [] and "X". Trace whether the invalid cast is diagnosed or reaches runtime; done means the code is consistently rejected with an error or executes successfully.