feat(tls): Add rustls-platform-verifier support

[tottoto]

Adds rustls-platform-verifier support.

[tottoto]

These are needed for macos and windows.

rustls/rustls-platform-verifier#133
rustls/rustls-platform-verifier#135

[tobz]

It would be good to get @djc's thoughts here, since the benefits listed by rustls-platform-verifier itself seem good, albeit small... and it's not clear to me if there are more and/or worse platform support caveats using this vs sticking with rustls-native-certs.

[djc]

As @tottoto suggested in a previous comment (thought it might not be quite clear), released versions of rustls-platform-verifier don't have all the API in place to support additivity with native-roots and webpki-roots across platforms, so might want to wait for that. The rustls project recommends ~all users migrate away from rustls-native-certs to using the rustls-platform-verifier.

rustls/rustls-platform-verifier#148

[LucioFranco]

Closing for now, feel free to reopen if we want to pick the work back up.

[TimOrtel]

What is the current status for this feature? I have a usecase where I need to support iOS and rustls-native-certs does not work (#1403). Using tls-webpki-roots is not a very good solution for me as I would not like to package certificates with an application, that could use the operating system certificates instead.

Is a workaround available with which it is somehow possible to inject rustls-platform-verifier while this feature is not merged?

Relevant for TimOrtel/GRPC-Kotlin-Multiplatform#60