Popover: deprecate the position prop

[ciampo]

Dev Note:

Following the recent refactors on the Popover component, the legacy position prop has been marked as deprecated. The newer placement prop should be used instead. The position prop is scheduled to be removed in WordPress 6.4.

What?

Add a deprecation warning for the position prop for the Popover component.

Note: this PR should only be merged once all instance of Popover in the repository have been migrated from using the position prop to the placement prop

Why?

With the refactor to floating-ui (#40740), a new placement prop was introduced to position the Popover. We should therefore remove the legacy position prop to avoid having two props achieving the same goal.

How?

Add a warning notice.

Preparatory work has been carried out in other PRs (see #42770 for more details)

Testing Instructions

Do a general smoke test across Gutenberg and:

• make sure that there are no deprecation warnings about the position prop written in the console
• make sure that all Popover instances keep behaving like on trunk

[getdave]

Removing Needs Dev Note label as this PR is not merged.