### What?
This PR fixes a minor issue in `richtext-lexical` where editor
placeholders were not localized.
### Why?
To allow users to localize placeholders accordingly with their language
preferences in config.
### How?
By evaluating the placeholder in the editor RSC, if any is provided. The
`ContentEditable` component falls back to a default in the event that no
placeholder was provided as this was the existing behavior.
Fixes#10518
dc6d79e76e