Handle implicit permits in turbine

[copybara-service]

Handle implicit permits in turbine

If the declaration of a sealed class C lacks a permits clause, then the permitted direct subclasses of C are as follows:

If C is not an enum class, then its permitted direct subclasses are those classes declared in the same compilation unit as C (§7.3) which have a canonical name (§6.7) and whose direct superclass is C.

That is, the permitted direct subclasses are inferred as the classes in the same compilation unit that specify C as their direct superclass. The requirement for a canonical name means that no local classes or anonymous classes will be considered.

https://docs.oracle.com/javase/specs/jls/se21/html/jls-8.html#jls-8.1.1.2