Update legacy tests to expect `TypeError` in place of `NullThrownError`

In Dart 3.0 `NullThrownError` has been removed and all expectations should be updated to expect a `TypeError` instead. This expectation is for legacy (pre-null safety) code as well.

These legacy tests need to be updated:
```
co19_2/Language/Expressions/Throw/evaluation_t04 
co19_2/LibTest/async/Future/Future.sync_A01_t03
co19_2/Utils/tests/Expect/throws_A01_t03
```

cc @eernstg 