[labs/react] Add back the reserved React property warning

[justinfagnani]

Should this be an RFC?

• This is not a substantial change

Which package is this a feature request for?

React (@lit-labs/react)

Description

#2800 removed our warning for reserved React property names because it changed how we detect custom element properties. We should add this back, but only in a dev build, which we'll need to set up for the react package.

Alternatives and Workarounds

n/a

[taylor-vann]

Curious if we can close this issue.

We don't iterate over the element like we didn't with #2800 which doesn't give us the opportunity to warn users about properties except for on component updates.