Reduce FileDescriptor memory usage

`FileDescriptors` keep intermediate state around, which is not needed after processing.

E.g. a single persistence.counters.proto FileDescriptor instance uses 967KB.

I'm not sure if the field documentation is useful for anything after the annotations have been parsed, but it is kept in memory, and in a hotrod-client test each DefaultCacheManager instance seem to need 3 instances of the string.
There is no native byte type in protobuf so it is mapped to int32. from the WrappedMessage.wrappedByte documentation.

Many lists are LinkedList instances, even though a LinkedList with 3 elements uses more memory than an ArrayList with 10 elements. Some lists are also wrapped in Collections$UnmodifiableRandomAccessList twice.

FileDescriptor HashMap fields (extendDescriptors, dependants) are never queried by key.

Start by profiling a FileDescriptor instance and tracing the intermediate state, field documentation, list implementations, wrapper lists, and HashMap fields named in the issue. Determine which data remains necessary after annotation parsing and whether the maps are queried. Done means reducing retained memory without breaking descriptor processing, with relevant tests or measurements confirming the behavior.

Written by the indexing model from the issue text.