Add a dart mcp-server command per go/dart-mcp-server-release-plan.

- Adds `dart_mcp` and `dart_mcp_server` as DEPS
- Build an AOT snapshot for the dart_mcp_server executable
- Add top level `mcp-server` command to dartdev (hidden).
- I also did add an `--experimental-mcp-server` flag which is required for this command to actually work. We had initially discussed not doing this due to complexity but I was able to keep it completely scoped to just this command. I can remove it if there are strong opinions though.

Change-Id: I737a5625507f69a904ccd1012682764eb360a2c2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/430900
Reviewed-by: Siva Annamalai <asiva@google.com>
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Jake Macdonald <jakemac@google.com>

pubspec.yaml

@@ -143,6 +143,10 @@ dependency_overrides:
     path: third_party/pkg/tools/pkgs/csslib
   dart_flutter_team_lints:
     path: third_party/pkg/ecosystem/pkgs/dart_flutter_team_lints
+  dart_mcp:
+    path: third_party/pkg/ai/pkgs/dart_mcp
+  dart_mcp_server:
+    path: third_party/pkg/ai/pkgs/dart_mcp_server
   dart_style:
     path: third_party/pkg/dart_style
   dartdoc:
@@ -221,6 +225,8 @@ dependency_overrides:
     path: third_party/pkg/tools/pkgs/pool
   protobuf:
     path: third_party/pkg/protobuf/protobuf
+  process:
+    path: third_party/pkg/tools/pkgs/process
   protobuf_benchmarks:
     path: third_party/pkg/protobuf/benchmarks
   protoc_plugin:
@@ -257,6 +263,8 @@ dependency_overrides:
     path: third_party/pkg/tools/pkgs/stack_trace
   stream_channel:
     path: third_party/pkg/tools/pkgs/stream_channel
+  stream_transform:
+    path: third_party/pkg/tools/pkgs/stream_transform
   string_scanner:
     path: third_party/pkg/tools/pkgs/string_scanner
   swift2objc: