Add support for specifying badEnclosingTypes for BadImport via flags

[copybara-service]

Add support for specifying badEnclosingTypes for BadImport via flags

Following the discussions in #2236, this PR introduces the BadImport:BadEnclosingTypes flag to disallow nested types of specified enclosing type.

This PR also takes the flag into account in UnnecessarilyFullyQualified to suggest importing EnclosingType.NestedType when possible.

For instance, when -XepOpt:BadImport:BadEnclosingTypes=org.immutables.value.Value is set, it would suggest the following:

final class Test {
  @org.immutables.value.Value.Immutable
  abstract class AbstractType {}
}

->

final class Test {
  @Value.Immutable
  abstract class AbstractType {}
}

Also, it won't require suppressing UnnecessarilyFullyQualified in the example in #2236.

import org.springframework.beans.factory.annotation.Value;

final class Test {
  Demo(@Value("some.property") String property) {}

  @org.immutables.value.Value.Immutable
  abstract class AbstractType {}
}

Closes #2236.

Fixes #4228

FUTURE_COPYBARA_INTEGRATE_REVIEW=#4228 from hisener:halil.sener/bad-import-bad-enclosing-types 67aa36d

[hisener]

@cushon can we merge this PR?

[cushon]

@cushon can we merge this PR?

It's waiting on an internal review before it can be merged, which I have pinged.