[lldb] Add Model Context Protocol (MCP) support to LLDB (#143628)

This PR adds an MCP (Model Context Protocol ) server to LLDB. For
motivation and background, please refer to the corresponding RFC:
https://discourse.llvm.org/t/rfc-adding-mcp-support-to-lldb/86798

I implemented this as a new kind of plugin. The idea is that we could
support multiple protocol servers (e.g. if we want to support DAP from
within LLDB). This also introduces a corresponding top-level command
(`protocol-server`) with two subcommands to `start` and `stop` the
server.

```
(lldb) protocol-server start MCP tcp://localhost:1234
MCP server started with connection listeners: connection://[::1]:1234, connection://[127.0.0.1]:1234
```

The MCP sever supports one tool (`lldb_command`) which executes a
command, but can easily be extended with more commands.

1 files changed, 2 insertions, 0 deletions

diff --git a/lldb/source/Interpreter/CommandInterpreter.cpp b/lldb/source/Interpreter/CommandInterpreter.cpp
index 4f9ae10..00c3472 100644
--- a/lldb/source/Interpreter/CommandInterpreter.cpp
+++ b/lldb/source/Interpreter/CommandInterpreter.cpp
@@ -30,6 +30,7 @@
 #include "Commands/CommandObjectPlatform.h"
 #include "Commands/CommandObjectPlugin.h"
 #include "Commands/CommandObjectProcess.h"
+#include "Commands/CommandObjectProtocolServer.h"
 #include "Commands/CommandObjectQuit.h"
 #include "Commands/CommandObjectRegexCommand.h"
 #include "Commands/CommandObjectRegister.h"
@@ -574,6 +575,7 @@ void CommandInterpreter::LoadCommandDictionary() {
   REGISTER_COMMAND_OBJECT("platform", CommandObjectPlatform);
   REGISTER_COMMAND_OBJECT("plugin", CommandObjectPlugin);
   REGISTER_COMMAND_OBJECT("process", CommandObjectMultiwordProcess);
+  REGISTER_COMMAND_OBJECT("protocol-server", CommandObjectProtocolServer);
   REGISTER_COMMAND_OBJECT("quit", CommandObjectQuit);
   REGISTER_COMMAND_OBJECT("register", CommandObjectRegister);
   REGISTER_COMMAND_OBJECT("scripting", CommandObjectMultiwordScripting);