[dart2bytecode, vm/interpreter] Small fixes

* Use AllocateClosure instruction for closure instantiations in order
  to initialize closure entry point.

* Fix null handling in operator== to be before argument type checks.

* Add _InvocationMirror._withType to dynamic interface as it is
  implicitly used by noSuchMethod forwarders.

* Fix AssertAssignable for null objects.

TEST=language tests in vm-aot-dyn-linux-debug-x64 configuration

Change-Id: I7b1a037d4fde4d22ed32969e0f099b31ea4432ab
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/382500
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>

utils/dynamic_module_runner/dynamic_interface.yaml

@@ -16,6 +16,11 @@ callable:
   - library: 'dart:core'
     class: '_Enum'
     member: ''
+  - library: 'dart:core'
+    class: '_InvocationMirror'
+  - library: 'dart:core'
+    class: '_InvocationMirror'
+    member: '_withType'
   - library: 'dart:core'
     class: '_GrowableList'
   - library: 'dart:core'