The change in [0] has propagated now everywhere, so we can use
`utf8.encode()` instead of the longer `const Utf8Encoder.convert()`.

Also it cleans up code like

```
  TypedData bytes;
  bytes.buffer.asByteData();
```

as that is not guaranteed to be correct, the correct version would be

```
  TypedData bytes;
  bytes.buffer.asByteData(bytes.offsetInBytes, bytes.lengthInBytes);
```

a shorter hand for that is:

```
  TypedData bytes;
  ByteData.sublistView(bytes);
```

[0] https://github.com/dart-lang/sdk/issues/52801