Split Codespaces configuration based on development scenarios

[eerhardt]

Taking advantage of the new "monorepo" projects feature in https://github.blog/changelog/2022-07-28-prebuilding-codespaces-is-now-supported-for-multi-repository-and-monorepo-projects/.

This allows us to have different Codespaces pre-builds based on what kind of work you are doing. It also minimizes the down-time of pre-builds if one development scenario is broken (for example if the WASM prebuild is broken, libraries developers can still use the libraries pre-build).

The duplication of the Dockerfile is unfortunate. But I'm thinking if we can move these docker images to https://github.com/dotnet/dotnet-buildtools-prereqs-docker, we could:

1. save time during the pre-build actions because the image doesn't need to be rebuilt every day.
2. Refactor the Dockerfiles into layers and reuse the common pieces.
   cc @MichaelSimons and @mthalman for thoughts on that.

This will require an admin to update the Codespaces in the Settings tab of the repo. I don't have access to do that.

[ghost]

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Issue Details

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Taking advantage of the new "monorepo" projects feature in https://github.blog/changelog/2022-07-28-prebuilding-codespaces-is-now-supported-for-multi-repository-and-monorepo-projects/.

This allows us to have different Codespaces pre-builds based on what kind of work you are doing. It also minimizes the down-time of pre-builds if one development scenario is broken (for example if the WASM prebuild is broken, libraries developers can still use the libraries pre-build).

The duplication of the Dockerfile is unfortunate. But I'm thinking if we can move these docker images to https://github.com/dotnet/dotnet-buildtools-prereqs-docker, we could:

1. save time during the pre-build actions because the image doesn't need to be rebuilt every day.
2. Refactor the Dockerfiles into layers and reuse the common pieces.
   cc @MichaelSimons and @mthalman for thoughts on that.

This will require an admin to update the Codespaces in the Settings tab of the repo. I don't have access to do that.

Author:	eerhardt
Assignees:	-
Labels:	area-Infrastructure-libraries
Milestone:	-

[MichaelSimons]

2. Refactor the Dockerfiles into layers and reuse the common pieces.
cc @MichaelSimons and @mthalman for thoughts on that.

I think that makes sense. You are installing a lot of common prereq packages that aren't going to change at a high frequency.

[ghost]

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[fanyang-mono]

WASM related change looks good to me! This is a great new feature. Now I could add the build for Mono desktop scenarios.

[eerhardt]

I have addressed all feedback and have manually tested this works in my fork. Once I merge, I'm going to need a repo admin to update the settings in order to get the Codespaces prebuilds working again.

I plan on merging tomorrow unless I get more feedback.

Feedback addressed