Storybook docs should not show current-value

[rajsite]

🐛 Bug Report

FormAssociated elements using the fast-foundation implementation end up with current-value attributes defined.

I believe current-value should only be considered internal and users shouldn't manipulate it directly or see it in code snippets. Currently it shows up in storybook code snippet docs for button unexpectedly (and potentially intermittently?).

💁 Possible Solution

• short-term can filter it out like we filter the class attribute
  • That current class filter tries to detect nimble- specifically, we could change it to just search for custom element name definitions generally
• long-term we should move off the form association polyfill in fast-foundation to the native feature