sets: adding clear-set.
hashtables: slightly faster grow logic.
compiler.cfg.alias-analysis: use clear-set.
hash-sets: faster implementation based on hashtables.
hashtables: reuse (rehash).
hash-sets: reuse (rehash).
bootstrap: make sure to rehash hash-sets also.
hash-sets: fix help-lint warnings.
benchmark.ant: fix hash-set constructor.
sets: adding union! and intersection.
sets: adding diff!.
vocabs.parser: use hash-sets in search-vocab-names.
classes: store implementors in hash-sets.
compiler: use hash-sets to track visited sets.
compiler: fix stack effects to indicate visited is same object.
compiler.tree.propagation.info: inline <value-info>.
compiler.cfg.ssa.construction: more use of hash-sets.
compiler.cfg.write-barrier: more use of hash-sets.
compiler.tree.recursive: more use of hash-sets.
compiler.cfg.loop-detection: more use of hash-sets.