Add useful trait impls

[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

Adds

• impl From<&dyn Reflect> for Value
• impl ToOwned for dyn Reflect

which I've found to be useful.