Error detection & messaging on joplin fields

When an author attempts to publish a page with a missing required field, they receive a user error and the offending field changes to an error state. However, it would be nicer if once the user began to input into the field that the state would revert to normal, rather than continuing to give the user a message. 

Fixing this would allow the design to accommodate the character limit in the same spot as the error message.

Start by reproducing the publish flow with a required Joplin field left empty, then enter text into the field after the validation error appears. Done means the field returns to its normal state as soon as input begins, while the character-limit message can occupy the same area as the error message.

Written by the indexing model from the issue text.