Restructure IMcpEndpoint, IMcpClient, and IMcpServer (#723)

* Remove `McpEndpoint` & `IMcpClient`

* Revise naming, add abstract classes

* Fix missing renames

* Move extension methods to instance methods

* Add back old API, but obsoleted

* Add back obsoleted factory classes

* Move deprecation attributes

* `SseClientTransport` -> `HttpClientTransport`

* Update src/ModelContextProtocol.Core/Server/AugmentedServiceProvider.cs

Co-authored-by: Stephen Halter <halter73@gmail.com>

* PR feedback

* PR feedback

* Add back dispose lock

* Fix docs projects

* PR feedback

* Undo `docs/*.md` changes

---------

Co-authored-by: Stephen Halter <halter73@gmail.com>

samples/ChatWithTools/Program.cs

@@ -32,7 +32,7 @@ using IChatClient samplingClient = openAIClient.AsIChatClient()
     .UseOpenTelemetry(loggerFactory: loggerFactory, configure: o => o.EnableSensitiveData = true)
     .Build();
 
-var mcpClient = await McpClientFactory.CreateAsync(
+var mcpClient = await McpClient.CreateAsync(
     new StdioClientTransport(new()
     {
         Command = "npx",