Use rustls for Swift to support TLS 1.3

Currently Element X iOS does not support TLS 1.3, this PR shall fix that.

Explanation:

There is an official recommendation from Apple, that boils down to the
following if you use cross-platform code with sockets (as we do with the rust sdk):

> To use TLS in that case [BSD Sockets], add your own TLS implementation.

> Don’t use Secure Transport for your TLS implementation. It’s been deprecated since 2019
> and doesn’t support TLS 1.3. If you have existing code that uses Secure Transport, make
> a plan to migrate off it.

Modern TLS implementations including TLS 1.3 on macOS are only available as a builtin
via the Apple-specific URLSession / Network framework APIs, so APIs where you feed in
an URL and get the response back. They are not available in combination with a generic
sockets-based cross-platform code.

With that in mind, there is currently no hope that rust-native-tls would support TLS 1.3
in the forseeable future as there is simply no native TLS implementation in current
macOS/iOS that could be used by rust-native-tls.

See https://developer.apple.com/documentation/technotes/tn3151-choosing-the-right-networking-api#TLS-best-practices

Fixes: element-hq/element-x-ios#786

bindings/matrix-sdk-ffi/Cargo.toml

@@ -57,7 +57,7 @@ language-tags = "0.3.2"
 log-panics = { version = "2", features = ["with-backtrace"] }
 paranoid-android = "0.2.1"
 
-[target.'cfg(target_os = "android")'.dependencies.matrix-sdk]
+[target.'cfg(any(target_os = "android", target_os = "ios", target_os = "macos"))'.dependencies.matrix-sdk]
 workspace = true
 features = [
     "anyhow",
@@ -72,7 +72,7 @@ features = [
     "uniffi",
 ]
 
-[target.'cfg(not(target_os = "android"))'.dependencies.matrix-sdk]
+[target.'cfg(not(any(target_os = "android", target_os = "ios", target_os = "macos"))'.dependencies.matrix-sdk]
 workspace = true
 features = [
     "anyhow",