docs: fix doc issues and header consistency

[TropicolX]

This PR addresses several minor issues in the TanStack Form documentation:

1. Basic Concepts Section:

   • Updated the snippet to use meta for errors and isValidating since they're not directly in field.state.
   • New snippet:

     const { value, meta: { errors, isValidating } } = field.state

2. Arrays Guide:

   • Changed "Basic usage" subtopic header from h1 to h2 for better consistency.

3. Linked Fields Guide:

   • Added an id and title to the markdown to match other sections.

Links to the issues:

• Basic Concepts
• Arrays Guide
• Linked Fields