Fix list array vs list discrepancies

[davidpdrsn]

Checklist

• [x] I have read the Contributor Guide
• [x] I have read and agree to the Code of Conduct
• [x] I have added a description of my changes and why I'd like them included in the section below

Description of Changes

This fixes a few issues with arrays that I discovered:

• <[T; N]>::from_reflect for Value::List would previously fail. It now works if the lengths match.
• Vec::as_array, Vec::as_array_mut, Vec::into_array now correctly return Some(_).
• Value::as_array, Value::as_array_mut, Value::into_array now correctly return Some(_) for Value::List.

Basically lists are a subtype of arrays so if something is a list then its also an array, i.e. as_array should work on a &dyn List.