[DDC] Add capability to detect whether an object is a library for custom formatting

[srujzs]

Currently, our custom formatter in DDC formats libraries only within the context of a module. Specifically, given a module, we recognize it as a special object using getModuleName:

sdk/sdk/lib/_internal/js_dev_runtime/private/debugger.dart

Line 628 in d05ea2f

name: name, value: Library(name, value!), hideName: true));

. Then, we know to use the custom formatter for that module. Given that, the module formatter explicitly creates a Library object to format each library within that module:

sdk/sdk/lib/_internal/js_dev_runtime/private/debugger.dart

Line 350 in d05ea2f

if (dart.isJsInterop(object) && dart.getModuleName(object) == null) {

. This then means that libraries are every formatted when a user inspects a module. When a user inspects a library, it is treated as just a JS object because we cannot detect whether it's a library.

With the new module format, this becomes even more important as we no longer have modules, only libraries. Once we add this capability to detect libraries, _useNativeJSFormatter should be updated. Similarly, debugger_test.dart should be updated to directly pass libraries instead of wrapping them in Librarys. See https://dart-review.googlesource.com/c/sdk/+/389589.