Update flutter_tools to look for new VM service message (#97683)

* Update flutter_tools to look for new VM service message

The Dart SDK will soon move away from the current Observatory message:

"Observatory listening on ..."

To a new message that no longer references Observatory:

"Dart VM Service listening on ..."

This change updates all tests with mocks to check for the new message
and also adds support for the new message in ProtocolDiscovery.

See https://github.com/dart-lang/sdk/issues/46756

* Fix some parsing locations

* Fix analysis failures

* Update message

* Remove extra comment

* Update message

* Add globals prefix