Each Node instance should have a type property for its concrete type

[litherum]

Migrated from https://bugs.webkit.org/show_bug.cgi?id=189611

On 2018-09-13 19:59:34 PDT, tdenney@apple.com wrote:
We should add an additional preparation stage that annotates each Node instance in the tree with its concrete type (i.e. not a TypeRef instance!). It doesn’t matter when this happens in the preparation so long as it happens after Checker.

[litherum]

On 2018-09-13 20:01:45 PDT, tdenney@apple.com wrote:
Ideally this phase should also assure that each user-defined/Array/ArrayRef type instance A that is equivalent to another instance B is identical to B.