* [flutter_tools] null safety mode is used for dill naming

* add bad test case

This reverts commit 66b01c1f.

* Add DDS ipv6 support

* Use --dds-port for DDS instead of hijacking --host-vmservice-port

This reverts commit c8f234d3.

This reverts commit 2436de13.

This reverts commit eef0050d.

* Reland "Re-enable the Dart Development Service (DDS) (#64671)"

This reverts commit 2ae25cc2.

* Fix MDNS building Observatory URI with port 0 instead of forwarding the device port

* Added MDNS test

This reverts commit d7d12412.

This change re-enables DDS and outputs the DDS URI in place of the VM
service URI on the console. If --disable-dds is not provided,
--host-vmservice-port will be used to determine the port for DDS rather
than the host port for the VM service, which will instead be randomly
chosen.

Also combines experiments into extraGenSnapshot/ExtraFrontEndOptions. Allows providing --no-sound-null-safety to allow out of order migration and running.

Support --enable-experiment in flutter test (for flutter_tester). Required minor change for null safety.

Fixes #51010

The test package differentiates between passing and not passing this
argument. A previous version had a bug that treated passing `0`
identically to not passing the argument, and the flutter test runner
relied on this bug by always passing a value and using a default of `0`.

- Remove the argument defaults throughout to make it clear that `null`
  is a valid value and the default.
- Remove the argument defaulting on the argument parser.
- Update the wording of the usage for this argument, this will also be
  updated on the `package:test` side.