Improve devcontainer file structure

[networkfusion]

Description

• Moves containers to seperate folders based on platform.
  Superseeds (part implementation of) Switch dev containers to seperate directories #2816

Motivation and Context

Although there are some futher changes I would like to make (in another PR), this moves the devcontainers to seperate directories which makes it easier for users to choose and develop against their respective platforms in a devcontainer.

It fixes the various issues raised against the last PR.

How Has This Been Tested?

• Was able to select and run the devcontainers locally.
• Smoke tests still pass (using the src files).
• Publishing the images needs to be checked on when merged.
• Documentation may need to be adjusted when merged. (see here: https://github.com/nanoframework/nanoframework.github.io/tree/networkfusion-devcontainers-patch)

Screenshots

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue with code or algorithm)
• New feature (non-breaking change which adds functionality to code)
• Breaking change (fix or feature that would cause existing functionality to change)
• Config and build (change in the configuration and build system, has no impact on code or features)
• Dev Containers (changes related with Dev Containers, has no impact on code or features)
• Dependencies (update dependencies and changes associated, has no impact on code or features)
• Documentation (changes or updates in the documentation, has no impact on code or features)

Checklist

• My code follows the code style of this project (only if there are changes in source code).
• My changes require an update to the documentation (there are changes that require the docs website to be updated).
• I have updated the documentation accordingly (the changes require an update on the docs in this repo).
• I have read the CONTRIBUTING document.
• I have tested everything locally and all new and existing tests passed (only if there are changes in source code).

[networkfusion]

@alberk8 Given I know that you use devcontainers, if you can also test this and add feedback, it would be welcome.

[alberk8]

@networkfusion, It works but rather annoying is that you need to select the Dev Container every time you reopen the container. Is it possible to have something like selecting the target where it will resists across Container restart?.

[Ellerbach]

hat will definitely be much cleaner! And I think the action should be adjusted, see my comment

[networkfusion]

@Ellerbach any response to the comments before merge?
@alberk8 I get it, but, the prompt to reopen the container at least makes sure that you are dealing with the correct container and has the benefit of making sure it is the latest version (whilst also more intuative for new users).

[Ellerbach]

any response to the comments before merge?

go ahead, nothing we can't correct later anyway ;-)