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.

servo-tidy.toml

@@ -48,6 +48,12 @@ packages = [
   "wayland-sys",
   "bitflags",
 
+  # Duplicated by rustls and image.
+  "spin",
+
+  # Duplicated by rustls and the version of webpki-roots required by async_tungstenite.
+  "rustls-webpki",
+
   # https://github.com/servo/servo/issues/26933
   "bytes",
   "futures",
@@ -112,7 +118,6 @@ files = [
   # Long encoded string
   "./tests/wpt/mozilla/tests/mozilla/resources/brotli.py",
   "./tests/wpt/webgl/meta/MANIFEST.json",
-  "./support/android/openssl.sh",
   # Upstream code from Khronos/WebGL uses tabs for indentation
   "./tests/wpt/webgl/tests",
   # Vendored from upstream