[FTS] the "Number of compaction bytes written" does not represent actual compaction progress

While the actual companion cycle is happening the corresponding stat is all zero until the cycle is done.

For higher loads/longer compaction cycles it looks like system is  idle. This is especially misleading during the initial indexing. It seems like indexing is stuck or crashed. Nothing is going on, all stats are silent for 10-20 seconds in some cases.

Also from debugging or performance tuning  perspective the stat  doesn't provide clear info on how big are the segments, how many, etc

Maybe something like "uncompacted bytes" or "index fragmentation %" would be better stat?