Allow quick_actions to register more than once

[Cretezy]

flutter/flutter#18864

[Hixie]

cc @mehmetf can you take a look to see if this patch makes sense?

[mehmetf]

This plugin is unique in the sense that no other plugin expects Android system to build an activity to interact with it (UrlLauncher comes close but does not expect to post anything to the channel).

I believe this is safe in the current embedder since the system is supposed to construct a new activity in the UI thread and we override the _channel value when the application is initialized. However, if we allow this plugin to be registered anywhere else, there's a risk that the activity will be constructed before the channel's value is set.

[mehmetf]

@Cretezy please take a look at my comments. We can merge this in after you fix the minor issues I pointed out.

[Cretezy]

@mehmetf I applied your suggestions. Let me know if everything is okay!

[mehmetf]

LGTM! Just fix the failing tests and you are good to go.

[mehmetf]

• build-ipas failure is unrelated to this. It does not touch any iOS files.
• The analysis failure is due to old git client. It has been fixed already (and this PR does not touch it).

Please also update changelog and pubspec.yaml. This should be a minor version bump.

[Cretezy]

@mehmetf should be good to go! Also, the failing build before was for formatting, not the ipas/git

[VadymPinchuk]

@mehmetf Hey guys, As I can see - currently a lot of plugins are outdated - changes are merged to plugins but new version are not published. Please fix that )
Interested in plugins: quick_actions and device_info

[mehmetf]

Done! Sorry about that.

[VadymPinchuk]

@mehmetf thank you a lot ;)