internal_isGroupLike

Helper to see if this is “group-like”. Edition 2024 will likely provide a new feature to better deal with this. See upsteam protobuf for more details on the problem.

Descriptor+Extensions.swift:136
var internal_isGroupLike: Bool { get }

This models upstream internal::cpp::IsGroupLike().

TODO(thomasvl): make this package instead of public and drop the “internal” part from the name when 5.9 is the baseline.