Add a mention of dot shorthands on the FWE layout page

[sfshaza2]

Page URL

https://docs.flutter.dev/get-started/fundamentals/layout

Page source

No response

Describe the problem

I don't want to forget, but the very first time in the new fundamentals doc, where we use the dot shorthands notation, mention it and link to the page on the dart.dev site: https://dart.dev/language/dot-shorthands

Expected fix

As stated above.

Additional context

No response

I would like to fix this problem.

• [ ] I will try and fix this problem on docs.flutter.dev.