Micro-optimizations to Plugin data to reduce minimum memory for Jenkins (#3654)

* Reduce memory footprint for the plugin info by presizing hashmaps to reduce waste for small maps and interning commonly duplicated plugin strings

* Replace duplicated empty string arrays with the one in MemoryReductionUtil

* Fix interning where strings are null

* Fix to deal with the fact that we directly mutate dependency fields for UpdateSite, sigh

* Reduce starting HashMap size for some hashmaps likely to be empty or tiny

* Cleanup per review comments

* Trim some extra waste out of the UpdateSite warnings

* Fix count of optional dependencies

* Move predicates for dependency matching to top-level static final field so they are not duplicated