feat(common): define public API surface for NgOptimizedImage directive

[AndrewKushnir]

This commit annotates a set of symbols exposed by the NgOptimizedImage directive as a public API.

PR Type

What kind of change does this PR introduce?

• [x] Feature

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

[AndrewKushnir]

This PR is blocked by PR #47024 that updates docs extraction logic to stop requiring an @ngModule doc tag on standalone types.

[angular-automatic-lock-bot[bot]]

This issue has been automatically locked due to inactivity. Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}