Create a dedicated reference page about creating a Flutter app

[parlough]

The CLI and a variety of pages need a dedicated page to link to learn more about creating a Flutter app, but we don't have one. If we know their desired creation method (CLI, IntelliJ, VS Code, IDX, etc) we do, but we often aren't sure in the references.

This page would likely be best as a reference, rather than a guide or tutorial.

It could potentially contain a reference of the available options, such as available templates, package name, target platforms, etc. Then a section for each method of creating a package/app:

• flutter create
• IntelliJ/Android Studio
• VS Code
• IDX
• Others?
• Cross-link to add to app docs for those cases

[parlough]

\cc @RedBrogdon @sfshaza2 A great candidate for a medium-size issue that gives an opportunity to try out a variety of Flutter-related tooling.

Adding this page would also help enable dropping some of the pages from the old get-started flow.