Make choice of sstable reader types explicit

CASSANDRA-9580 made it apparent that the efforts to isolate unsafe users of early opened results wasn't quite fully successful.

This patch attempts to impose some minor central refactors that force the (internal) user to specify if they want the live sstable set, or the "canonical" sstable set (or just the "noncompacting" set, since this is the intersection of the two). It also eliminates a lot of ugliness and some duplication around filtration, and obsoletes the CANONICAL_SSTABLES and UNREPAIRED_SSTABLES functions in ColumnFamilyStore, which were very ugly.