Moved analyzer tests to its own project

Also moves tests to `./test` which makes it possible
for all test projects to share the same .editorconfig
files and similar.

test/Spectre.Console.Analyzer.Tests/CodeFixProviderDiscovery.cs

@@ -0,0 +1,55 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.VisualStudio.Composition;
+using Spectre.Console.Analyzer.FixProviders;
+
+namespace Spectre.Console.Analyzer.Tests
+{
+    internal static class CodeFixProviderDiscovery
+    {
+        private static readonly Lazy<IExportProviderFactory> _exportProviderFactory;
+
+        static CodeFixProviderDiscovery()
+        {
+            _exportProviderFactory = new Lazy<IExportProviderFactory>(
+                () =>
+                {
+                    var discovery = new AttributedPartDiscovery(Resolver.DefaultInstance, isNonPublicSupported: true);
+                    var parts = Task.Run(() => discovery.CreatePartsAsync(typeof(SystemConsoleToAnsiConsoleFix).Assembly)).GetAwaiter().GetResult();
+                    var catalog = ComposableCatalog.Create(Resolver.DefaultInstance).AddParts(parts);
+
+                    var configuration = CompositionConfiguration.Create(catalog);
+                    var runtimeComposition = RuntimeComposition.CreateRuntimeComposition(configuration);
+                    return runtimeComposition.CreateExportProviderFactory();
+                },
+                LazyThreadSafetyMode.ExecutionAndPublication);
+        }
+
+        public static IEnumerable<CodeFixProvider> GetCodeFixProviders(string language)
+        {
+            var exportProvider = _exportProviderFactory.Value.CreateExportProvider();
+            var exports = exportProvider.GetExports<CodeFixProvider, LanguageMetadata>();
+            return exports.Where(export => export.Metadata.Languages.Contains(language)).Select(export => export.Value);
+        }
+
+        private class LanguageMetadata
+        {
+            public LanguageMetadata(IDictionary<string, object> data)
+            {
+                if (!data.TryGetValue(nameof(ExportCodeFixProviderAttribute.Languages), out var languages))
+                {
+                    languages = Array.Empty<string>();
+                }
+
+                Languages = ((string[])languages).ToImmutableArray();
+            }
+
+            public ImmutableArray<string> Languages { get; }
+        }
+    }
+}