Add automated leak detection for common scenarios

[JakeWharton]

There are common scenarios that occur in Redwood and Treehouse which we should use to ensure branches of the graph are correctly GC'd.

Examples:

• Remove a composable from RedwoodView composition and the associated view should be GC'd
• Cancel Redwood composition and the entire composition and all views should go
• Remove a composable from within Treehouse and the associated view should be GC'd
• New code is loaded using Treehouse and all old views should go
• Cancel Treehouse and the entire JS VM and TreehouseView subtype should go

We need to be able to do this on every platform we support.

On Android and JVM we can use LeakCanary. On JS and native we can just do what leak canary is doing: create a weak reference and spin for 5 seconds to see if the reference disappears, optionally trying to force a GC as much as possible (if possible).

[JakeWharton]

https://kotlinlang.org/docs/native-memory-manager.html#enable-garbage-collection-manually

[JakeWharton]

For JS we could do https://stackoverflow.com/a/3034245/132047. We are currently using Chromium for tests, but desire to switch to Node.js, in which case it's still V8 so basically the same thing works: https://stackoverflow.com/a/30654451/132047

[swankjesse]

This came up again today. We could use the XCTest memory leak detection magic. The test should create a LazyList and bind it and confirm nothing leaks

https://developer.apple.com/documentation/xcode/preventing-memory-use-regressions

[JakeWharton]

Still want to do:

• RedwoodView / TreehouseView
• WidgetSystem

[JakeWharton]

• child views after code reload