TF-3450 Add text attachment preview

core/lib/domain/preview/supported_preview_file_types.dart

@@ -5,6 +5,11 @@ class SupportedPreviewFileTypes {
     'image/gif',
     'image/png',];
 
+  static const textMimeTypes = [
+    'text/plain',
+    'text/markdown',
+  ];
+
   static const docMimeTypes = [
     'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
     'application/vnd.oasis.opendocument.text',

core/lib/presentation/extensions/media_type_extension.dart

@@ -21,6 +21,8 @@ extension MediaTypeExtension on MediaType {
 
   bool isRtfFile() => SupportedPreviewFileTypes.rtfMimeTypes.contains(mimeType);
 
+  bool isTextFile() => SupportedPreviewFileTypes.textMimeTypes.contains(mimeType);
+
   DocumentUti getDocumentUti() => DocumentUti(SupportedPreviewFileTypes.iOSSupportedTypes[mimeType]);
 
   String getIcon(ImagePaths imagePaths, {String? fileName}) {