CFE: support interfaces and mixins for enum classes

[alexmarkov]

This is a part of #47453.

Tests co19/LanguageFeatures/Enhanced-Enum/semantics_A01_t01 and co19/LanguageFeatures/Enhanced-Enum/semantics_A01_t02 fail with RuntimeError on the VM because interfaces and mixins are currently ignored for enum classes.

For the enum class which is declared as

enum E with M implements I1, I2 {

the following kernel is generated by CFE:

  class E extends core::_Enum /*isEnum*/  {

@chloestefantsova Could you please take a look?

[chloestefantsova]

Yes, this is the functionality I'm working on at the moment. The support for mixins was added yesterday: https://dart-review.googlesource.com/c/sdk/+/227541. Currently I'm looking into supporting interfaces: https://dart-review.googlesource.com/c/sdk/+/228161/.