Add Codespaces container definitions for the VMR (#15172)

Resolves https://github.com/dotnet/arcade/issues/11902

src/SourceBuild/content/.devcontainer/devcontainer.json

@@ -0,0 +1,17 @@
+// Container contains checked-out source code only
+{
+    "name": "Default",
+    "image": "mcr.microsoft.com/dotnet-buildtools/prereqs:fedora-36",
+    "hostRequirements": {
+        // A completely built .NET source-tarball is >64 GB
+        "storage": "128gb"
+    },
+    "customizations": {
+        "vscode": {
+            "extensions": [
+                "ms-dotnettools.csharp",
+                "eamodio.gitlens"
+            ]
+        }
+    }
+}

src/SourceBuild/content/.devcontainer/prebuilt-sdk/build.sh

@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+
+source="${BASH_SOURCE[0]}"
+scriptroot="$( cd -P "$( dirname "$source" )" && pwd )"
+
+"$scriptroot"/../../prep.sh
+
+# GitHub Codespaces sets this and it conflicts with source-build scripts.
+unset RepositoryName
+
+"$scriptroot"/../../build.sh --online --clean-while-building || exit 0

src/SourceBuild/content/.devcontainer/prebuilt-sdk/devcontainer.json

@@ -0,0 +1,18 @@
+// Container contains a pre-built SDK
+{
+    "name": "Pre-built .NET SDK",
+    "image": "mcr.microsoft.com/dotnet-buildtools/prereqs:fedora-36",
+    "hostRequirements": {
+        // A completely built .NET source-tarball is >64 GB
+        "storage": "128gb"
+    },
+    "customizations": {
+        "vscode": {
+            "extensions": [
+                "ms-dotnettools.csharp",
+                "eamodio.gitlens"
+            ]
+        }
+    },
+    "onCreateCommand": "${containerWorkspaceFolder}/.devcontainer/prebuilt-sdk/build.sh"
+}

src/SourceBuild/content/eng/bootstrap/README.template.md

@@ -135,6 +135,10 @@ tar -zxf artifacts/x64/Release/dotnet-sdk-8.0.100-centos.8-x64.tar.gz -C $HOME/.
 ln -s $HOME/.dotnet/dotnet /usr/bin/dotnet
 ```
 
+### Codespaces
+
+You can also utilize [GitHub Codespaces](https://github.com/features/codespaces) where you can find preset containers in this repository.
+
 ## List of components
 
 To enable full offline source-building of the VMR, we have no other choice than to synchronize all the necessary code into the VMR. This also includes any code referenced via git submodules. More details on why and how this is done can be found here: