[mini_types] Add a `Type.substitute` method.

This method will be used by a follow-up CL that adds support for
generic functions, since the implementation of `==` and `hashCode` for
generic functions needs to perform substitutions in order to recognize
that alpha-equivalent types (such as `T Function<T>()` and `U
Function<U>`) are equal.

Change-Id: If641c4d0ae48708abf3701853014dc52dfc559c5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/395684
Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

https://dart.googlesource.com/sdk/+/58f9beb6d4ec9e93430454bb96c0b8f068d0b0bc

DEPS

diff --git a/DEPS b/DEPS
index f793be7..3b73393 100644
--- a/DEPS
+++ b/DEPS
@@ -260,7 +260,7 @@
 
   'engine/src/flutter': Var('flutter_git') + '/mirrors/engine' + '@' + '9686de154114bc3f487aec34ba0a4f6a8a6358ef',
 
-  'engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + 'e1c76b280528ad05ac58b29fd543e5b30622ed1f',
+  'engine/src/flutter/third_party/dart': Var('dart_git') + '/sdk' + '@' + '58f9beb6d4ec9e93430454bb96c0b8f068d0b0bc',
 
   'flutter': Var('flutter_git') + '/mirrors/flutter' + '@' + 'b3818f6b59791da804d203775710f7b4e3a439e0',
 

commits.json

diff --git a/commits.json b/commits.json
index 48220ae..be59f0a 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "engine/src/flutter":"9686de154114bc3f487aec34ba0a4f6a8a6358ef",
-  "engine/src/flutter/third_party/dart":"e1c76b280528ad05ac58b29fd543e5b30622ed1f",
+  "engine/src/flutter/third_party/dart":"58f9beb6d4ec9e93430454bb96c0b8f068d0b0bc",
   "flutter":"b3818f6b59791da804d203775710f7b4e3a439e0"
 }
\ No newline at end of file