Update content according to latest spec (#513)

* Update content according to latest spec

* Add Title to a bunch of types

* Add _meta to lots of types

* Address feedback, more cleanup, fix NAOT test failure

src/ModelContextProtocol.Core/Protocol/IBaseMetadata.cs

@@ -0,0 +1,25 @@
+using System.Text.Json.Serialization;
+
+namespace ModelContextProtocol.Protocol;
+
+/// <summary>Provides a base interface for metadata with name (identifier) and title (display name) properties.</summary>
+public interface IBaseMetadata
+{
+    /// <summary>
+    /// Gets or sets the unique identifier for this item.
+    /// </summary>
+    [JsonPropertyName("name")]
+    string Name { get; set; }
+
+    /// <summary>
+    /// Gets or sets a title.
+    /// </summary>
+    /// <remarks>
+    /// This is intended for UI and end-user contexts. It is optimized to be human-readable and easily understood,
+    /// even by those unfamiliar with domain-specific terminology.
+    /// If not provided, <see cref="Name"/> may be used for display (except for tools, where <see cref="ToolAnnotations.Title"/>, if present, 
+    /// should be given precedence over using <see cref="Name"/>).
+    /// </remarks>
+    [JsonPropertyName("title")]
+    string? Title { get; set; }
+}