Switch to rustls and webpki-roots (#30025)

This change replaces OpenSSL with rustls and also the manually curated
CA certs file with webpki-roots (effectively the same thing, but as a
crate).

Generally speaking the design of the network stack is the same. Changes:

- Code around certificate overrides needed to be refactored to work with
  rustls so the various thread-safe list of certificates is refactored
  into `CertificateErrorOverrideManager`
- hyper-rustls takes care of setting ALPN protocols for HTTP requests,
  so for WebSockets this is moved to the WebSocket code.
- The safe set of cypher suites is chosen, which seem to correspond to
  the "Modern" configuration from [1]. This can be adjusted later.
- Instead of passing a string of PEM CA certificates around, an enum is
  used that includes parsed Certificates (or the default which reads
  them from webpki-roots).
- Code for starting up an SSL server for testing is cleaned up a little,
  due to the fact that the certificates need to be overriden explicitly
  now. This is due to the fact that the `webpki` crate is more stringent
  with self-signed certificates than SSL (CA certificates cannot used as
  end-entity certificates). [2]

1. https://wiki.mozilla.org/Security/Server_Side_TLS
2. https://github.com/briansmith/webpki/issues/114

Fixes #7888.
Fixes #13749.
Fixes #26835.
Fixes #29291.

components/net/tests/resource_thread.rs

@@ -4,6 +4,7 @@
 
 use crate::create_embedder_proxy;
 use ipc_channel::ipc;
+use net::connector::CACertificates;
 use net::resource_thread::new_core_resource_thread;
 use net::test::parse_hostsfile;
 use net_traits::CoreResourceMsg;
@@ -27,7 +28,8 @@ fn test_exit() {
         MemProfilerChan(mtx),
         create_embedder_proxy(),
         None,
-        None,
+        CACertificates::Default,
+        false, /* ignore_certificate_errors */
     );
     resource_thread.send(CoreResourceMsg::Exit(sender)).unwrap();
     receiver.recv().unwrap();