docs: Revamp MAUI quickstart

[kailash-b]

Description

This PR revamps the existing MAUI Quickstart to match the latest format and structure conventions.

Checklist

• I've read and followed CONTRIBUTING.md.
• I've tested the site build for this change locally.
• I've made appropriate docs updates for any code or config changes.
• I've coordinated with the Product Docs and/or Docs Management team about non-trivial changes.

[github-actions]

Summary

Status	Count
🔍 Total	9
✅ Successful	4
⏳ Timeouts	0
🔀 Redirected	1
👻 Excluded	4
❓ Unknown	0
🚫 Errors	0
⛔ Unsupported	0

Redirects per input

Redirects in main/docs/quickstart/native/maui/index.mdx

• [200] https://dotnet.microsoft.com/download | Redirect: Followed 1 redirect resolving to the final status of: OK. Redirects: https://dotnet.microsoft.com/download --> https://dotnet.microsoft.com/en-us/download
  Full Github Actions output