Plugin "default implementation" warnings on latest Flutter

[gnprice]

Building the app, or running flutter test or even just flutter pub get, produces the following warnings when using the latest Flutter from main — often several times over:

Package file_picker:linux references file_picker:linux as the default plugin, but it does not provide an
inline implementation.
Ask the maintainers of file_picker to either avoid referencing a default implementation via `platforms: linux:
default_package: file_picker` or add an inline implementation to file_picker via `platforms: linux:`
`pluginClass` or `dartPluginClass`.


Package flutter_local_notifications:linux references flutter_local_notifications_linux:linux as the default
plugin, but the package does not exist.
Ask the maintainers of flutter_local_notifications to either avoid referencing a default implementation via
`platforms: linux: default_package: flutter_local_notifications_linux` or create a plugin named
flutter_local_notifications_linux.


Package file_picker:macos references file_picker:macos as the default plugin, but it does not provide an
inline implementation.
Ask the maintainers of file_picker to either avoid referencing a default implementation via `platforms: macos:
default_package: file_picker` or add an inline implementation to file_picker via `platforms: macos:`
`pluginClass` or `dartPluginClass`.


Package file_picker:windows references file_picker:windows as the default plugin, but it does not provide an
inline implementation.
Ask the maintainers of file_picker to either avoid referencing a default implementation via `platforms:
windows: default_package: file_picker` or add an inline implementation to file_picker via `platforms:
windows:` `pluginClass` or `dartPluginClass`.

It looks like the warnings were introduced in:

• feat: Support overriding native endorsed plugins flutter/flutter#137040

Upstream issues in those plugins are:

• Already fixed, so we just need to upgrade: I was told to ask you to either avoid a reference or create a plugin (I am serious :) MaikuB/flutter_local_notifications#2368
• Filed by me just now: Default plugins for linux/macos/windows need to register implementation; warning on latest Flutter miguelpruivo/flutter_file_picker#1555

These are warnings, not errors, so don't seem to be blocking us. And they only apply to desktop platforms, not our real targets, so there should be no impact in production. The warning spew is annoying, though, so it'll be good to clear them up.