Forms guides

This first batch publishes 4 of the 27 upstream Forms guides; the rest are converted and will be released in later batches.

• Animated Select Picker — Create a custom select component whose dropdown is animated. For example, the menu fades or slides into view, or the options animate upon selection.
• Build a sign-in form that follows best practice — Build a sign-in form with correct autocomplete values and autofill support.
• SMS OTP form verification — Verify user phone numbers and one-time passcodes delivered over SMS with automatic code extraction and accessible form input.
• Validate Input After Interaction — Show form field validation feedback (e.g. password complexity or email format requirements) only after the user has finished their initial interaction, avoiding premature errors on page load or while the user is typing.