[analyzer][Class modifiers] No error if base class is indirectly implemented

[sgrekhov]

The following co19 tests fail in both analyzer and CFE
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Class-modifiers/basic_restrictions_A03_t08.dart
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Class-modifiers/basic_restrictions_A03_t09.dart
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Class-modifiers/basic_restrictions_A03_t10.dart

The code looks like

// class_modifiers_lib.dart
base class BaseClass {}

// test.dart
import "class_modifiers_lib.dart";

base class ExtendsBaseClass extends BaseClass {}

base class IndirectlyImplementsBaseClass implements ExtendsBaseClass {}
//                                                  ^^^^^^^^^^^^^^^^
// [analyzer] unspecified
// [cfe] unspecified

No expected errors produced. But according to the spec

It's a compile-time error if:
...
A declaration implements another declaration, and the other declaration itself, or any of its super-declarations, are marked base or final and are not from the first declaration's library

Tested on the edge SDK (April 17, 2023) on Linux x64

[eernstg]

If this is handled by _fe_analyzer_shared then 'area-meta' may be actionable. If it is handled separately by the common front end and the analyzer then we should have a sub-issue for each of those tools.

@johnniwinther, @stereotype441, WDYT?

[eernstg]

@kallentu, maybe you're the one who knows best?

[stereotype441]

@eernstg FYI, I recently created an area-fe-analyzer-shared label for issues affecting the shared code. I'll apply that label to this issue now. (@kallentu I don't actually know if you implemented this logic in a shared way or not; feel free to adjust the labels as appropriate).

[kallentu]

It's not shared code, but I just used the front end and analyzer labels. I'm okay if we want to split the issue or keep as is.
I'll look into the issue.

[eernstg]

Sounds good! We'd have two-or-more issues in the case where a given implementation effort takes place in two-or-more different portions of source code, because it's difficult to determine the right time to close the issue if one job is done and another is not. I guess that's not important in this case.

[scheglov]

Was fixed as #52160.