[mcp] Support MCP Apps part 3 - Add mcp tool call support. (#17364)

- [x] Add a new app-server method so that MCP Apps can call their own
MCP server directly.

codex-rs/app-server-protocol/schema/json/v2/McpServerToolCallResponse.json

@@ -0,0 +1,22 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "properties": {
+    "_meta": true,
+    "content": {
+      "items": true,
+      "type": "array"
+    },
+    "isError": {
+      "type": [
+        "boolean",
+        "null"
+      ]
+    },
+    "structuredContent": true
+  },
+  "required": [
+    "content"
+  ],
+  "title": "McpServerToolCallResponse",
+  "type": "object"
+}