SI-7321 Memory leak in specialize on multiple compiler runs.

Currently the map is declared LinkedHashMap, which doesn't align with
other caching maps that are cleared on every run. Linkedness is only
needed to ensure deterministic order on the generated specialized
classes. The same can be accomplished by sorting generated classes
a-posteriori.
Merge pull request #2351 from vigdorchik/ticket/si-7321b

SI-7321 Memory leak in specialize on multiple compiler runs.