Loading Native Certs on MacOS

[ansg191]

Currently, the TLS Context loads native root CA certs on Windows & Linux, but does not load CA certs on macOS.

MacOS native certs can be loaded using the security-framework crate (which is what rustls-native-certs uses).

A potential problem is that the Apple Security Framework has to be dynamically linked. This would be transparent for users using this as a rust crate or dynamically linking. But it would require users statically linking to quiche to manually link with the Security Framework.

Would this be something worth adding? And if the dynamic linking is a problem, could this be added as a cargo feature to make it opt-in?