Ensure order of destroyed methods for LayoutViews makes sense

[jamesplease]

Right now, the RegionManager has its own destroy method that is executed at around same time that a LayoutView's destroy method is. But instead of the LayoutView intelligently wrapping the destroy method so that the two before: destroys are side-by-side, it fires them one after the other, so that it goes

before:destroy, destroy, before:destroy, destroy.

Given that the RegionManager's events might be gone in v3, this might resolve itself automatically. But this is for us to make sure that the event order makes sense.

Reference #1753 for more.

[jamesplease]

Added to #1796.