Decompress pages on scan if compression config is disabled

If compression is disabled after being enabled for a while, then pages may remain compressed if they are not evicted and/or compacted. This can add the decompress overhead to scans. To avoid this, if a scan sees a compressed page, it should be decompressed.

Note that if tryPageSwapin decompresses a page, it must not compress it after swapin. If this is not handled, we may run into MB-50063