[dart2bytecode, vm/interpreter] Late final fields and variables

* Also, add implicitly overridden _Enum._enumToString to dynamic
  interface.

TEST=ci (vm-aot-dyn-linux-debug-x64)

Change-Id: I9d9d368715d0837d8b1039a46451152e03be7eec
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/383024
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Alexander Markov <alexmarkov@google.com>

utils/dynamic_module_runner/dynamic_interface.yaml

@@ -9,6 +9,9 @@ extendable:
 
 can-be-overridden:
   - library: 'dart:*'
+  - library: 'dart:core'
+    class: '_Enum'
+    member: '_enumToString'
 
 callable:
   - library: 'dart:*'