vinyl: use uncompressed run size for range split/coalesce/compaction

Historically, when considering splitting or coalescing a range or
updating compaction priority, we use sizes of compressed runs (see
bytes_compressed). This makes the algorithms dependent on whether
compression is used or not and how effective it is, which is weird,
because compression is a way of storing data on disk - it shouldn't
affect the way data is partitioned. E.g. if we turned off compression
at the first LSM tree level, which would make sense, because it's
relatively small, we would affect the compaction algorithm because
of this.

That said, let's use uncompressed run sizes when considering range
tree transformations.