[4.x] Prevent Bard causing dirty state issues

[duncanmcclean]

After doing some digging into #9294, I managed to track down Bard as the culprit of the dirty state issues.

After an entry is saved, the publish form values get updated. This consequently triggers Bard's value to be updated, which causes Bard to think it's json has changed and it needs to emit the updated value upwards.

However... in comparing the string-ified JSON with the actual value being passed into Bard, they were exactly the same. Yet, because it was emitted up the chain, it triggered the dirty state.

This only seems to be an issue when you have a few different sets open because it needs to take over 360ms (the timeout on PublishForm@runAfterSaveHook) to parse the JSON, stringify it again and do whatever else it needs to do, before the setTimeout re-enables the dirty state tracking.

I've put this fix directly into the BardFieldtype. However, let me know if you'd prefer this to be fixed in the Fieldtype mixin instead.

Fixes #9294.