phases: sparsify phase lists When the internal and archived phase was added, allphase became a large, sparsely populated list. This dramatically increased the number of lookup operations for public relations in `phasecache.phase`. As a first step, define allphases and related lists explicitly to contain only the actual phases. Make phasenames a dictionary and create corresponding dictionaries for mapping phase names back to numbers. Adjust various list to be sparse as well with the exception of phaseroots and phasesets members of phasecache. Keep those as a separate step as it involves changes to the C module. Differential Revision: https://phab.mercurial-scm.org/D8697