Skip emitting provided inner classes redundantly in `processUnprovidedTypes()`

[teppeis]

Fix for https://github.com/angular/clutz/pull/822

If an inner class has a non-class-like prop (ex. enum) and the prop is referenced from other jsdoc, the prop is emitted duplicately each time it is referred.

There are the examples in closure-library:

• goog.net.WebChannel.FailureRecovery.State
• goog.net.WebChannel.FailureRecovery.FailureCondition
• goog.proto2.TextFormatSerializer.Tokenizer_.Token
• goog.proto2.TextFormatSerializer.Tokenizer_.TokenTypes

Also added a test case for goog.debug.Trace that has a special structure related this handling.