Replace custom Platform & PlatformChecker with package platform

[vaind]

Description

Replace:

• dart/lib/src/platform/platform.dart
• dart/lib/src/platform_checker.dart

with https://pub.dev/packages/platform

Update: we've done some improvements/refactors in PlatformChecker but this issue is blocked until dart officially adds support for web as well, see dart-lang/core#862

[denrase]

@vaind Hey! Just started this and i'm seeing that example_web_compile_test.dart fails, as a file in the package uses dart:io

https://github.com/dart-lang/core/blob/main/pkgs/platform/lib/src/interface/local_platform.dart

Not sure how to circumvent this. Any suggestions?

[ueman]

You should be checking for "kIsWeb" (or do the same check in Dart code) before using the platform package.

[buenaflor]

You should be checking for "kIsWeb" (or do the same check in Dart code) before using the platform package.

we can definitely work around this but then we'd still have to use the existing impl for web so not sure if it's worth it to use it? wdyt

[vaind]

Any suggestions?

Is there a branch I can have a look at?

[denrase]

@vaind Pushed the code i had locally. Pretty much replaced our Platform definition in favour of package:platform/platform.dart, but here we have the issue that dart:io is used.