LibWeb: Implement 'Is secure context' AO

Author: https://github.com/linusg
Commit: 4baf0a4486
Pull-request: https://github.com/SerenityOS/serenity/pull/15795
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/davidot ✅

Userland/Libraries/LibWeb/HTML/Scripting/Environments.h

@@ -143,5 +143,6 @@ JS::Realm& relevant_realm(JS::Object const&);
 EnvironmentSettingsObject& relevant_settings_object(JS::Object const&);
 EnvironmentSettingsObject& relevant_settings_object(DOM::Node const&);
 JS::Object& relevant_global_object(JS::Object const&);
+[[nodiscard]] bool is_secure_context(Environment const&);
 
 }