[Suggestion][HxSubmit/any] More verbose exception details

[jolaquai]

At first, I thought my <EditForm> was the issue and I spent like 10 minutes trying to find out why I was even getting that exception.

Perhaps the messages could be rephrased (to include it's an HxButton's OnValidClick handler we're in) or maybe prefixed with where it's coming from, since the call stacks resulting from the RenderTreeBuilder can be a bit... indecipherable at times. Besides, I'm pretty sure not everyone has "Show external code" enabled in the Call Stack window or "Enable Just My Code" turned off AND symbols loaded to even reach the actual line throwing the exception.