[ VM / DDS / CLI ] Add DevTools support to the standalone VM

Example output on stdout when DevTools is enabled:

Observatory listening on http://127.0.0.1:8181/CzkZzZaONW4=/
The Dart DevTools debugger and profiler is available at: http://127.0.0.1:8181/devtools/#/?uri=ws%3A%2F%2F127.0.0.1%3A8181%2FCzkZzZaONW4%3D%2Fws
hello world!

vm-service: isolate(1674461414267555)  'main' has no debugger attached and is paused at exit.  Connect to Observatory at http://127.0.0.1:8181/CzkZzZaONW4=/ to debug.

TEST=pkg/dartdev/test/commands/run_test.dart

Change-Id: Icd1afda87ad4a46f228125d53094d10adf8056ec
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/188361
Commit-Queue: Ben Konyi <bkonyi@google.com>
Reviewed-by: Siva Annamalai <asiva@google.com>

utils/dartdev/BUILD.gn

@@ -2,12 +2,14 @@
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
+import("../../build/dart/copy_tree.gni")
 import("../application_snapshot.gni")
 
 group("dartdev") {
   public_deps = [
     ":copy_dartdev_kernel",
     ":copy_dartdev_snapshot",
+    ":copy_prebuilt_devtools",
   ]
 }
 
@@ -39,3 +41,15 @@ application_snapshot("generate_dartdev_snapshot") {
   deps = [ "../dds:dds" ]
   output = "$root_gen_dir/dartdev.dart.snapshot"
 }
+
+copy_trees("copy_prebuilt_devtools") {
+  sources = [
+    {
+      target = "copy_prebuilt_devtools"
+      visibility = [ ":dartdev" ]
+      source = "../../third_party/devtools/web"
+      dest = "$root_out_dir/devtools"
+      ignore_patterns = "{}"
+    },
+  ]
+}