First kotlin

Convert one class to kotlin and provide a slight amount of guidance.

Test: existing tests
Change-Id: Ie8659765b674ac7b2d82ed3d343f387195c07d83

packages/SystemUI/docs/kotlin-in-sysui.md

@@ -0,0 +1,22 @@
+# Kotlin in SystemUI
+
+Queue "it's happening" gif.
+
+Kotlin is probably going to be a bit of a wild west for a while, but please
+try to follow these guidelines as much as possible.
+
+ - No semi-colons: they are optional, we probably don't want them in the
+   future, so let's just not add them.
+ - No DSLs: sysui is complicated enough as is, let's not add more layers at
+   the moment.
+ - Only use extension functions for keeping complex code locality: Don't use
+   extension functions to add methods to android classes that you always wished
+   were there, instead add them directly to the class and save us the extension.
+ - inline, reified, and de-compisition can all be great things: just make sure
+   you know what they do and why you are using them.
+
+# Recommended reading
+
+ - [Kotlin](https://kotlinlang.org/)
+ - [AndroidX-KTX](https://www.youtube.com/watch?v=st1XVfkDWqk)
+ - [Performance and Kotlin tricks](https://www.youtube.com/watch?v=6P20npkvcb8)