This reverts commit 275ab9c6.

Revert "Reland "Remove references to Observatory (#118577)""

This reverts commit 298d8c76.

This reverts commit 2df140f4.

Observatory is being deprecated for Dart 3.0 so it should no longer be
referenced in tooling messaging / flags.

See https://github.com/dart-lang/sdk/issues/50233

This reverts commit 254a796b.

Revert "Reland "Add --serve-observatory flag to run, attach, and test (#118402)" (#119529)" (#119729)

This reverts commit 7477d7ac.

* Reland "Add --serve-observatory flag to run, attach, and test (#118402)"

This reverts commit 86ab01d2.

* Fix flaky failures

* Fix VM service disappearing failure

This reverts commit 6cd4fa45.

This flag will allow for Observatory to be served by the VM service once it is disabled by default in the Dart SDK.

* Use `dart __deprecated_pub` instead of `pub` to invoke pub from tools

The top level `pub` commmand has been deprecated and will print
a message. It is however implemented via the __deprecated_pub command
that prints no message.

* Add 'v' hotkey to open DevTools in the browser

[flutter_tools] refactor devtools handler to expose single method for run/attach and restart (#75807)