Port applyClassNameBindings to use attr nodes

[mixonic]

applyClassNameBindings is slow. It should be ported to use streams and an attr node. Related to #9921, but class name bindings are their own weird world. The class name bindings code in general should be consolidated- the same steps are repeated in the each/collection helper, in bind-attr, and in applyClassNameBindings.

The bind-attr implementation has been ported already.

[rwjblue]

@mixonic - I believe that this is something you are working on currently, c/d?

[mixonic]

Focusing on attr bindings re: #9921, but after that this will be a piece of cake.

[rwjblue]

attributeBindings landed in #10186. I believe that this is next on the chopping block.

[rwjblue]

Closing this, as I believe that AttrNode's are gone in Glimmer world.