[dart2wasm] Make cid numbering of concrete classes perfect DFS pre-order

The CL removes a hack that assigned fixed class ids due to the need of
special treatment for masquerading types.

=> Instead of hard coding the type category values, we discover feasible
slots automatically, so we can remove the hack
=> Makes our cid numbering of concrete classes pure DFS pre-order
=> Ensures all concrete subclasses of a class have continious class ids

We also replace an assembly stub that deals with masquerading with one
written in Dart, adding the necessary primitives (e.g.
getting category type table & kinds).

We also align how to get the function type of a closure, namely
add `_Closure._getClosureRuntimeType()` analogous to the method on
`_Record._getRecordRuntimeType()`

Change-Id: I5169fc4953e8e99c4f84a1bbe8e535c08fb47cc5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/348840
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>

https://dart.googlesource.com/sdk/+/a2ee738dfcb60e92e8ac196b085cfec8918dc85f

DEPS

diff --git a/DEPS b/DEPS
index 006cd5d..52f1507 100644
--- a/DEPS
+++ b/DEPS
@@ -281,7 +281,7 @@
 
   'engine/src/flutter': Var('flutter_git') + '/mirrors/engine' + '@' + '3d87470655b1ee076582faaf0960ebb192df9746',
 
-  'engine/src/third_party/dart': Var('dart_git') + '/sdk' + '@' + '41128c56e2880263268d7204d59615a2c8d7d525',
+  'engine/src/third_party/dart': Var('dart_git') + '/sdk' + '@' + 'a2ee738dfcb60e92e8ac196b085cfec8918dc85f',
 
   'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '44ce0bf95650a76d383625cb0008384ca4b4cdc9',
 

commits.json

diff --git a/commits.json b/commits.json
index fac460e..2be827a 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "engine/src/flutter":"3d87470655b1ee076582faaf0960ebb192df9746",
-  "engine/src/third_party/dart":"41128c56e2880263268d7204d59615a2c8d7d525",
+  "engine/src/third_party/dart":"a2ee738dfcb60e92e8ac196b085cfec8918dc85f",
   "flutter":"44ce0bf95650a76d383625cb0008384ca4b4cdc9"
 }
\ No newline at end of file