Add test for missing Xamarin SDKs

Author: mbg

csharp/ql/integration-tests/all-platforms/diag_missing_xamarin_sdk/diagnostics.expected

@@ -0,0 +1,48 @@
+{
+  "attributes": {},
+  "helpLinks": [],
+  "internal": false,
+  "location": {},
+  "markdownMessage": "CodeQL was unable to build the following projects using .NET Core:\n- `test.csproj`\nSet up a [manual build command](https://docs.github.com/en/code-security/code-scanning/automatically-scanning-your-code-for-vulnerabilities-and-errors/configuring-the-codeql-workflow-for-compiled-languages).",
+  "severity": "error",
+  "source": {
+    "extractorName": "csharp",
+    "id": "csharp/autobuilder/dotnet-build-failure",
+    "name": "Some projects or solutions failed to build using .NET Core"
+  },
+  "visibility": {
+    "statusPage": true
+  }
+}
+{
+  "attributes": {},
+  "helpLinks": [],
+  "internal": false,
+  "location": {},
+  "markdownMessage": "CodeQL was unable to build the following projects using MSBuild:\n- `test.csproj`\nSet up a [manual build command](https://docs.github.com/en/code-security/code-scanning/automatically-scanning-your-code-for-vulnerabilities-and-errors/configuring-the-codeql-workflow-for-compiled-languages).",
+  "severity": "error",
+  "source": {
+    "extractorName": "csharp",
+    "id": "csharp/autobuilder/msbuild-build-failure",
+    "name": "Some projects or solutions failed to build using MSBuild"
+  },
+  "visibility": {
+    "statusPage": true
+  }
+}
+{
+  "attributes": {},
+  "helpLinks": [],
+  "internal": false,
+  "location": {},
+  "markdownMessage": "[Configure your workflow](https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-xamarin-applications) for this SDK before running CodeQL.",
+  "severity": "error",
+  "source": {
+    "extractorName": "csharp",
+    "id": "csharp/autobuilder/missing-xamarin-ios-sdk",
+    "name": "Missing Xamarin SDK for iOS"
+  },
+  "visibility": {
+    "statusPage": true
+  }
+}

csharp/ql/integration-tests/all-platforms/diag_missing_xamarin_sdk/test.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <LanguageTargets>$(MSBuildExtensionsPath)\Xamarin\iOS\Xamarin.iOS.CSharp.targets</LanguageTargets>
+  </PropertyGroup>
+
+</Project>

csharp/ql/integration-tests/all-platforms/diag_missing_xamarin_sdk/test.py

@@ -0,0 +1,5 @@
+from create_database_utils import *
+from diagnostics_test_utils import *
+
+run_codeql_database_create([], db=None, lang="csharp", runFunction=runUnsuccessfully)
+check_diagnostics()