[flutter_tools] use initially parsed package config for language version, sound mode determination (#70323)

Fixes #69416
Fixes #70121

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

* add bad test case

* [flutter_test] handle breaking change to test main . Fixes #67382

Use the new single `src/platform.dart` import to pick up what is needed
to implement a test platform from both `test_api` and `test_core`.

* Set DDS port to requested observatory port for test

* Add test for DDS and observatory ports

* Use FakePlatform instead of mock, fix spacing

* Use FakeProcessManager instead of mock

* Fix analyze issue

* Make completer private and add fn for future

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.

This reverts commit 8b52e6a8.

This reverts commit adc9dde3.

- Fixed issue where `FallbackDiscovery` would hold on to a `VmService` when launching on iOS devices, causing DDS to fail to start
- Fixed `flutter drive` case where DDS is already running in another flutter_tools instance

Revert "Reland "Add support for Dart Development Service (DDS) in Flutter Tools (#61276)" (#61975)" (#61993)

This reverts commit f7a1c87f.

This reverts commit 4867f593.

Revert "Reland "Add support for Dart Development Service (DDS) in Flutter Tools (#61276)" (#61882)" (#61909)

This reverts commit 895b7ef6.

This reverts commit 38fe8873.

Revert "Reland "Add support for Dart Development Service (DDS) in Flutter Tools (#61276)" (#61633)" (#61641)

This reverts commit 594c3541.

This reverts commit a1a5a8f6.

Revert "Reland "Add support for Dart Development Service (DDS) in Flutter Tools (#61276)" (#61395)" (#61498)

This reverts commit f98184e4.

This reverts commit 5b9c6e2b.

This reverts commit fe7bbf72.

[flutter_tools] ensure generated entrypoint matches test and web entrypoint language version (#59291)

Ensure that the language version of the test/web generated entrypoint matches the language version of the test file to run, or the overall package language version if no annotation is provided.

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