Switch EditorFactory methods over to taking a IContentType

The overloads sometimes had exportProvider first and sometimes second.
This was because if you always had it first and content type is passed
as a string, you have ambiguity of how to handle the params array.
Just passing in stuff explicitly makes this easier.

Also replace a hand-written implementation of string.Join with
string.Join.

src/EditorFeatures/CSharpTest/Formatting/FormattingEngineTestBase.cs

@@ -74,8 +74,8 @@ protected async Task AssertFormatAsync(string expected, string code, IEnumerable
 
             // create new buffer with cloned content
             var clonedBuffer = EditorFactory.CreateBuffer(
-                buffer.ContentType.TypeName,
                 workspace.ExportProvider,
+                buffer.ContentType,
                 buffer.CurrentSnapshot.GetText());
 
             var formattingRuleProvider = workspace.Services.GetService<IHostDependentFormattingRuleFactoryService>();

src/EditorFeatures/TestUtilities/EditorFactory.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System.Text;
+#nullable enable
+
 using Microsoft.CodeAnalysis.Editor.UnitTests;
 using Microsoft.VisualStudio.Composition;
 using Microsoft.VisualStudio.Text;
@@ -16,55 +17,42 @@ public static class EditorFactory
             ExportProvider exportProvider,
             params string[] lines)
         {
-            return CreateBuffer("text", exportProvider, lines);
+            var contentType = exportProvider.GetExportedValue<ITextBufferFactoryService>().TextContentType;
+
+            return CreateBuffer(exportProvider, contentType, lines);
         }
 
         public static ITextBuffer CreateBuffer(
-            string contentType,
             ExportProvider exportProvider,
+            IContentType contentType,
             params string[] lines)
         {
             var text = LinesToFullText(lines);
-            var intContentType = exportProvider.GetExportedValue<IContentTypeRegistryService>().GetContentType(contentType);
-            var buffer = exportProvider.GetExportedValue<ITextBufferFactoryService>().CreateTextBuffer(intContentType);
-            buffer.Replace(new Span(0, 0), text);
-            return buffer;
+            return exportProvider.GetExportedValue<ITextBufferFactoryService>().CreateTextBuffer(text, contentType);
         }
 
         public static DisposableTextView CreateView(
             ExportProvider exportProvider,
             params string[] lines)
         {
-            return CreateView("text", exportProvider, lines);
+            var contentType = exportProvider.GetExportedValue<ITextBufferFactoryService>().TextContentType;
+            return CreateView(exportProvider, contentType, lines);
         }
 
         public static DisposableTextView CreateView(
-            string contentType,
             ExportProvider exportProvider,
+            IContentType contentType,
             params string[] lines)
         {
             WpfTestRunner.RequireWpfFact($"Creates an {nameof(IWpfTextView)} through {nameof(EditorFactory)}.{nameof(CreateView)}");
 
-            var buffer = CreateBuffer(contentType, exportProvider, lines);
+            var buffer = CreateBuffer(exportProvider, contentType, lines);
             return exportProvider.GetExportedValue<ITextEditorFactoryService>().CreateDisposableTextView(buffer);
         }
 
         public static string LinesToFullText(params string[] lines)
         {
-            var builder = new StringBuilder();
-            var isFirst = true;
-            foreach (var line in lines)
-            {
-                if (!isFirst)
-                {
-                    builder.AppendLine();
-                }
-
-                isFirst = false;
-                builder.Append(line);
-            }
-
-            return builder.ToString();
+            return string.Join("\r\n", lines);
         }
     }
 }

src/EditorFeatures/TestUtilities/Workspaces/TestWorkspace_XmlConsumption.cs

@@ -203,7 +203,7 @@ public static TestWorkspace Create(string xmlDefinition, bool completed = true,
                 var contentTypeLanguageService = languageServices.GetService<IContentTypeLanguageService>();
 
                 var contentType = contentTypeLanguageService.GetDefaultContentType();
-                var textBuffer = EditorFactory.CreateBuffer(contentType.TypeName, exportProvider, code);
+                var textBuffer = EditorFactory.CreateBuffer(exportProvider, contentType, code);
 
                 // The project
 
@@ -748,7 +748,7 @@ private static CompilationOptions CreateCompilationOptions(TestWorkspace workspa
             // For linked files, use the same ITextBuffer for all linked documents
             if (!filePathToTextBufferMap.TryGetValue(filePath, out var textBuffer))
             {
-                textBuffer = EditorFactory.CreateBuffer(contentType.TypeName, exportProvider, code);
+                textBuffer = EditorFactory.CreateBuffer(exportProvider, contentType, code);
                 filePathToTextBufferMap.Add(filePath, textBuffer);
             }
 
@@ -793,7 +793,7 @@ private static CompilationOptions CreateCompilationOptions(TestWorkspace workspa
             var documentServiceProvider = GetDocumentServiceProvider(documentElement);
             var contentTypeLanguageService = languageServiceProvider.GetService<IContentTypeLanguageService>();
             var contentType = contentTypeLanguageService.GetDefaultContentType();
-            var textBuffer = EditorFactory.CreateBuffer(contentType.TypeName, exportProvider, code);
+            var textBuffer = EditorFactory.CreateBuffer(exportProvider, contentType, code);
 
             return new TestHostDocument(
                 exportProvider, languageServiceProvider, textBuffer, filePath: string.Empty, cursorPosition, spans, codeKind, folders, isLinkFile: false, documentServiceProvider, roles: roles);

src/EditorFeatures/VisualBasicTest/Formatting/VisualBasicFormatterTestBase.vb

@@ -28,7 +28,7 @@ Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.UnitTests.Formatting
                 Dim buffer = workspace.Documents.First().GetTextBuffer()
 
                 ' create new buffer with cloned content
-                Dim clonedBuffer = EditorFactory.CreateBuffer(buffer.ContentType.TypeName, workspace.ExportProvider, buffer.CurrentSnapshot.GetText())
+                Dim clonedBuffer = EditorFactory.CreateBuffer(workspace.ExportProvider, buffer.ContentType, buffer.CurrentSnapshot.GetText())
 
                 Dim document = workspace.CurrentSolution.GetDocument(hostdoc.Id)
                 Dim syntaxTree = Await document.GetSyntaxTreeAsync()