Reland "[ddc] Overhauling tearoff equality and identity."

This new update adds fixes + tests for cross-module super mixins. Super getters can refer to mixins compiled in other modules, so we need to expose all mixin names to make them accessible from their enclosing library.

This is a reland of commit e4c4d0f839ce4998a46ac3997aea2668d3edd48f

Original change's description:
> [ddc] Overhauling tearoff equality and identity.
>
> Hot reload requires DDC to update how its tearoffs are represented. Tearoffs obey the following conventions:
> * Instance tearoffs are never identical
> * Tearoffs with the same object target and name have the same hash code (even if they resolve to different functions across hot reloads)
> * Two separate tearoffs of the same member are equal
>
> To support this, tearoff equality must not depend on the bound object and method but a composite of the bound object, torn off member name, and the exact class/object from which the member was torn off.
>
> Notable changes:
> * Methods' immediately bound targets are emitted with member signatures. This is required to determine the bound targets for instance and dynamic tearoffs. Bound targets are identified by `libraryUri:class` strings.
> * `applyMixin` passes in a 'true' bound target. This is because mixin applications' members are considered children of their 'on' class (not the mixed in class) wrt equality/hashCode.
> * `bind` is modified to pass in its 'true' bound object to support mixins' super getters.
> * `tearoff` and `staticTearoff` are modified to accept a bound target string (only required for static tearoffs, as they are bound at tearoff-creation-time).
> * Static tearoffs avoid using their bound object for hashcode and equality, as these libraries may be wrapped in proxy objects.
> * Tearoff equality and hashCode are updated to consider bound object, bound name, and its bound method's immediate target.
> * 'noSuchMethod' and 'toString' methods are always accessed through their extension property during signature lookups.
>
>
> Change-Id: Ica5501b6860c605db50aa945bafb6802a7317511
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/406723
> Reviewed-by: Nate Biggs <natebiggs@google.com>
> Reviewed-by: Nicholas Shahan <nshahan@google.com>
> Commit-Queue: Mark Zhou <markzipan@google.com>

Change-Id: I645992030f9106c158426412387ddecafc78e3f4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/415102
Reviewed-by: Nate Biggs <natebiggs@google.com>
Commit-Queue: Mark Zhou <markzipan@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>

https://dart.googlesource.com/sdk/+/ba90daf304abb446be20816709adee709d7b1021

DEPS

diff --git a/DEPS b/DEPS
index e1e0bc9..ea90126 100644
--- a/DEPS
+++ b/DEPS
@@ -234,7 +234,7 @@
 ]
 
 deps = {
-  'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + 'fd3eaa68318850697eb610483b8f8f866c28cdc6',
+  'flutter/engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + 'ba90daf304abb446be20816709adee709d7b1021',
 
   'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + '082a761570e89f67a56f50de1c4cb843a2e452af',
 

commits.json

diff --git a/commits.json b/commits.json
index 1753f04..1969b25 100644
--- a/commits.json
+++ b/commits.json
@@ -1,4 +1,4 @@
 {
   "flutter":"082a761570e89f67a56f50de1c4cb843a2e452af",
-  "flutter/engine/src/flutter/third_party/dart":"fd3eaa68318850697eb610483b8f8f866c28cdc6"
+  "flutter/engine/src/flutter/third_party/dart":"ba90daf304abb446be20816709adee709d7b1021"
 }
\ No newline at end of file