Add adaptation information for text fields

[InMatrix]

• Publish a guide on flutter/uxr
  • [Feedback Requested] Cross-platform Adaptation for Text Field uxr#95
• Add a TL;DR to https://docs.flutter.dev/resources/platform-adaptations#ui-components

[atsansone]

@InMatrix : What did you have in mind for the TL;DR? I'm not 100% sure what the dev would need to do from flutter/uxr#95. Thanks!

[InMatrix]

@atsansone Thanks for the ping. Developers will be able to customize a Material TextField into an iOS-like TextField using the snippets from flutter/uxr#95.

I haven't got around to complete the second task on the list yet.