This PR adds a test that reproduces the problem described in the linked issue: hot restart on the web seems to not update if the app being run is `const`.

The new test is expected to fail, until the `const` issue with hot restart in the web is resolved.

Expected failure mode is a 15s timeout in the following test:

```
02:31 +3 ~1 -1: Hot reload (index.html: Default) (with `const MyApp()`)): newly added code executes during hot restart [E]
  TimeoutException after 0:00:15.000000: Future not completed
  dart:async  _startMicrotaskLoop
  ...
```

(And then a bunch of output that I'm not 100% sure is intended :))

## Issues

* #141588