[kbn/optimizer] Remove usage of extraPublicDir

[spalger]

In #68986 we added the ability to export more than just the public dir of a plugin via the extraPublicDir config in kibana.json. This was intended as a temporary solution until we no longer need to export more than public and could automatically export common. In the meantime we can probably work towards this by removing extraPublicDir where possible and adding a uiCommon flag or something to specifically activate sharing of the common dir.

There are a couple intricacies with this though:

1. not all common dirs are intended for public use
2. not all common dirs can be imported in the browser as-is. In some cases the common dir stored config schemas that can be imported by the browser as long as only the types are consumed, consuming the whole schema throws errors as the version of Joi we use is not compatible with the browser.

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)

[joshdover]

Related to #59710

[tylersmalley]

This will be replaced by #128012