Use a debugging flag that doesn't keep the process running on exit

See dart-lang/sdk#24352

Author: wkillerud

docs/contributing/testing-and-debugging.md

@@ -25,7 +25,7 @@ You should also turn off extensions like SCSS IntelliSense or Some Sass.
 
 ### Open the Dart DevTools
 
-In this configuration, the client has run `dart run --observe` in the local `sass_language_server` package. You can now use [Dart DevTools](https://dart.dev/tools/dart-devtools) to debug the language server.
+In this configuration, the client has run `dart run --enable-vm-service` in the local `sass_language_server` package. You can now use [Dart DevTools](https://dart.dev/tools/dart-devtools) to debug the language server.
 
 To find the link to open Dart DevTools, use the `[Extension Development Host]`.
 

extension/src/server.ts

@@ -46,7 +46,7 @@ export async function createServerOptions(
     args: [
       'run',
       // '--pause-isolates-on-start', // Uncomment this to debug issues during startup and initial scan
-      '--observe',
+      '--enable-vm-service',
       'sass_language_server',
       '--loglevel=debug',
     ],