PyList: add more sequence APIs

[birkenfeld]

See #1845

Since these are just literal copies of the sequence methods, this makes me think - could PyList deref to PySequence?

[birkenfeld]

Now also forwarding the methods to PySequence instead of copy-pasting the impl.

[davidhewitt]

Thanks, I've definitely come around to this being the right thing to do.

Since these are just literal copies of the sequence methods, this makes me think - could PyList deref to PySequence?

It's tempting, however I've been wondering also whether we should have Python types Deref to their Python base, just like what web-sys does. PyList deref to PySequence doesn't fit that pattern.

How about adding .as_sequence() method, and maybe even impl AsRef<PySequence> for PyList? That would also be useful within the implementation of these methods?

Also, needs CHANGELOG entry 😄

[davidhewitt]

Thanks, this looks good to me! I still think .as_sequence() could be useful, however I'm happy to see that as a separate PR...