Fix #4316: add text editor interfaces.

Oqtane.Shared/Interfaces/ITextEditor.cs

@@ -0,0 +1,22 @@
+using System.Threading.Tasks;
+
+namespace Oqtane.Interfaces
+{
+    /// <summary>
+    /// Text editor interface.
+    /// </summary>
+    public interface ITextEditor
+    {
+        /// <summary>
+        /// initializes the editor with the initialize content.
+        /// </summary>
+        /// <param name="content">the initialize content.</param>
+        void Initialize(string content, bool updated); 
+
+        /// <summary>
+        /// get content from the editor.
+        /// </summary>
+        /// <returns></returns>
+        Task<string> GetContent();
+    }
+}