Allow modules to run code during autolinking (to capture unmet implicit dependencies/requirements)

[asklar]

Sometimes a community module will have requirements for the app to consume it successfully.
For example:

• the react-native-print module requires that the app define a XAML Canvas element named RNPrintCanvas.
• similarly, use of inking will require the app to set IsPerspectiveEnabled=false
• C# modules require C++ apps to add the consumecsharpmodules property (this already works automatically)

In the case of react-native-print, this is documented in the module's readme, but it would be good if there was a way for the module to express requirements or even run some JS during autolink to either (in pri order):

1. print a message explaining module requirements on the app
2. check whether the condition is satisfied and if not print a message
3. check the condition and fix it for the user

[acoates-ms]

In 0.64 react-native doctor should be pluggable. At which point community modules would be able to provide their own checks. Maybe that would be a way to do this?

This doesn't seem like a react-native-windows specific issue.

[chrisglein]

The goal would be to have as much automatic validation as possible so that errors are caught proactively. Being able to diagnose after the fact is good too, but maybe we can fail faster?

[jaimecbernardo]

Another related issue is that modules may want to plug into some application events.
One example is react-native-splash-screen, which extends the splash screen.
The windows implementation would benefit from being able to hook into the Application.OnLaunched event to get Splash Screen information, as it's the supported way of doing this on Windows: https://docs.microsoft.com/en-us/windows/uwp/launch-resume/create-a-customized-splash-screen