chore: [DSYS-616] create/update Input migration docs

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Description

Add migration documentation for Input by comparing legacy Extension and Mobile source APIs against MMDS React/RN Input APIs, then documenting the explicit mapping and examples.

Changes included:

• Added Input Component section to packages/design-system-react/MIGRATION.md with structured breaking-change mapping and before/after extension examples.
• Added Input Component section to packages/design-system-react-native/MIGRATION.md with structured mapping and before/after mobile examples.
• Added migration links in both Input READMEs:
  • packages/design-system-react/src/components/Input/README.mdx
  • packages/design-system-react-native/src/components/Input/README.md

Validation gate status:

• Ran yarn lint:fix and yarn lint from repo root.
• Both fail due to existing repo-wide Tailwind lint violations in unrelated files (262 tailwindcss/no-custom-classname errors).

DSYS_EPIC: DSYS-616
MIGRATION_DOCS_VERSION: 22f3e4c

Related issues

Fixes: DSYS-636

Manual testing steps

1. Open packages/design-system-react/MIGRATION.md and confirm TOC includes Input Component and the section contains structured API mapping + extension before/after examples.
2. Open packages/design-system-react-native/MIGRATION.md and confirm TOC includes Input Component and the section contains structured API mapping + mobile before/after examples.
3. Open both Input README files and confirm they include migration links to their respective MIGRATION.md#input-component anchors.
4. Run yarn lint:fix and yarn lint to reproduce current lint baseline failures.

Screenshots/Recordings

Before

N/A (docs-only update)

After

N/A (docs-only update)

Pre-merge author checklist

• I've followed MetaMask Contributor Docs
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

  

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