Feature request: add conditional display support to HelpBox #134

Summary

Would you consider extending HelpBox so it can be conditionally shown?
Right now, HelpBox appears to work independently from attributes like ShowIf / HideIf. In some cases this can leave a help box visible even when the related field is hidden, which makes the inspector a bit confusing.

Use case

I use HelpBox to guide users toward safer usage patterns.
For example, I want to warn when an untyped reference is being used, but only in the same context where that field is actually visible.

Current limitation

HelpBox currently seems to support:

• message
• message type
  But it does not appear to support its own visibility condition.

Requested functionality

It would be very helpful if HelpBox could optionally respect a condition, for example:

[HelpBox("Prefer the typed version when possible", HelpBoxMessageType.Warning, nameof(ShouldShowWarning))]