Read library glide module names from Java indexes

[sjudd]

Progress for #5043

Annotation processors (including ksp) only run on newly compiled code. Libraries have been previously compiled, so an annotation processor will not be run on them. To find any LibraryGlideModules included in those libraries, we look for specific generated classes in those libraries that we call Indexes. Indexes contain an annotation listing the class names of any LibraryGlideModules. Indexes are generated by Glide's annotation processors for each library and are exported as part of the library.

To preserve the package private visibility of the existing Java Index annotation, I created a new Index annotation for the KSP processor. This lets us reference the KSP Index annotation directly.

Unfortunately it also means that the Java and KSP Index classes are not the same. While it's only a small amount of duplicated code, it's a significant compatibility issue because the KSP and Java processors no longer produce the same Index class.

In particular the KSP processor looks only for its Index class and not for the Java processor's Index class. This is unfortunate because Glide's libraries are always processed by the Java annotation processor, not the KSP processor. In turn this means that Glide's KSP processor effectively ignores any of Glide's integration libraries.

To fix this in the short term I've made the KSP processor look for both its Indexes and the Java annotation processors Indexes. A more robust fix would be to merge the two Index processors so that the annotation processors are mutually compatible. I'll do that in a follow-up.

I've written tests, but they're somewhat involved so I'll send them as a follow-up.