reshape: STCS: preserve token contiguity when reshaping disjoint sstables
reshape: STCS: preserve token contiguity when reshaping disjoint sstables

When reshaping hundreds of disjoint sstables, like on bootstrap,
contiguity wasn't being preserved because the heuristic for picking
candidates didn't take into account their token range, which resulted
in reshape messing with the contiguity that could otherwise be
preserved by respecting the token order of the disjoint sstables.
In other words, sstables with the smallest first tokens should be
compacted first. By doing that, the contiguity is preserved even
across size tiers, after reshape has completed its possible multiple
rounds to get all the data in shape.

Signed-off-by: Raphael S. Carvalho <1e2942cea40e3b4d2162dfcd9e53e41c05a84d22@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla