[Platform.is*] Using of Platform.isAndroid or Platform.isIOS should either be deprecated or documentation should be clear

[AbhishekDoshi26]

We all know that using Platform.isAndroid and Platform.isIOS crashes on web because these constants lie inside dart:io which is not supported for web and many times no one really checks which file was imported due to the usage of something.

But, many less experienced developers keep on using these for multi-platform apps because they are habitual to use it. We already have an alternative i.e. to lay down the if-else such that it checks for web first. Or, we can also use defaultTargetPlatform == TargetPlatform.android as this works on all platforms.

I propose either of the following:

• Deprecate Platform.is* so that we don't make silly mistakes
• Properly mention in the documentation that this should not be used in projects with web implementations.

This will really help developers to not make silly mistakes of using Platform.is* in multi-platform projects.

Note: Opened similar issue in dart-lang repo too.

[mraleph]

/cc @lrhn @mit-mit

[stuartmorgan]

See https://github.com/dart-lang/io/issues/93#issuecomment-1371372964 for some issues with the claims here.

(Filing three copies of the same issue in different repositories makes discussion really difficult; please just pick one location in the future.)

[mraleph]

Ping @mit-mit @lrhn. Do we have an issue somewhere which reflects our plans for platform detection improvements? I would like to either label this issue or close it in favor of existing issue.