Implement console.clear

[jdm]

Spec: https://console.spec.whatwg.org/#clear
Code: components/script/dom/console.rs

We'll need some new devtools integration for this.

[mustafapc19]

Hi. I am new-comer to this. But I think I might be able to do this if I was given some additional resources and a little bit of help navigating the codebase.

[jdm]

• the WebIDL in components/script/dom/webidls/Console.webidl
• the DOM implementation in components/script/dom/console.rs
• the script->devtools integration in components/devtools_traits/lib.rs
• the devtools server in components/devtools/actors/console.rs

We need our devtools server code in to send a ConsoleAPI message with a level value of "clear", according to https://searchfox.org/mozilla-central/rev/cf561cece0ca9aeaf0202e68699836d957d0c670/devtools/client/webconsole/utils/messages.js#134-148. That means we need to send a message to the devtools server from the console.rs code when Console::Clear is called.

You can test these changes following https://github.com/servo/servo/wiki/Devtools and connecting to an instance of Servo from the Firefox remote devtools.

Please ask questions if anything is unclear!

[mustafapc19]

U can assign me for this. I'll ask questions if I find some roadblocks. And thanks for your imput :).