make devcontainer work with unpublished sdks (#18847)

Author: Martin521

.devcontainer/devcontainer.json

@@ -1,12 +1,12 @@
 // For format details, see https://aka.ms/vscode-remote/devcontainer.json or this file's README at:
 {
     "name": "F#",
-    "image": "mcr.microsoft.com/dotnet/sdk:10.0.100-preview.3",
+    "image": "mcr.microsoft.com/dotnet/sdk:9.0.304",
     "features": {
-        "ghcr.io/devcontainers/features/common-utils:2.5.3": {},
-        "ghcr.io/devcontainers/features/git:1.3.3": {},
+        "ghcr.io/devcontainers/features/common-utils:2.5.4": {},
+        "ghcr.io/devcontainers/features/git:1.3.4": {},
         "ghcr.io/devcontainers/features/github-cli:1.0.14": {},
-        "ghcr.io/devcontainers/features/dotnet:2.2.1": {}
+        "ghcr.io/devcontainers/features/dotnet:2.3.0": {}
     },
     "hostRequirements": {
         "cpus": 2,
@@ -28,7 +28,8 @@
         }
     },
     "remoteEnv": {
-        "TARGET": "net9.0"
+        "FSHARPCORE_USE_PACKAGE": "false",
+        "PATH": "${localWorkspaceFolder}/.dotnet:${containerEnv:PATH}"
     },
-    "postCreateCommand": [ "dotnet", "build", "FSharp.Compiler.Service.sln"]
+    "postCreateCommand": [ "bash", "-c", "eng/common/dotnet.sh && cp -r .dotnet/sdk/* /usr/share/dotnet/sdk && cp -r .dotnet/shared/Microsoft.NETCore.App/* /usr/share/dotnet/shared/Microsoft.NETCore.App" ]
 }