Avoid clobbering existing field prefix, descriptions, and label suffix values

I think a general overhaul of how we're adding the message is called for. In order to avoid clobbering existing field prefix, description fields and/or label suffix fallbacks.

This refactor should also support appending/prepending to keyed render arrays, plain strings and FormattableMarkup objects in a generalized way.

jwilson3 → credited maskedjellybean → .

Automatically closed - issue fixed for 2 weeks with no activity.