This reverts commit 8b6baae4.

Our current top crasher is an unclear error when ProcessManager fails to resolve an executable path. To fix this, we'd like to being adjusting the process resolution logic and adding more instrumentation to track failures. In order to begin the process, the ProcessManager has been folded back into the flutter tool

* opt out the flutter tool

* oops EOF

* fix import

* Update tool_backend.dart

* Update daemon_client.dart

* fix more

* [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.