KYLIN-3656 Improve HLLCounter performance

[hit-lacus]

The current HLLCounter implementation has some room to improve performance, as we find in our product environment. Improvement related to getCountEstimate of HLLCounter and constructor of HLLCounter.

• Create HLLCounter from another HLLCounter, we can copy register(using System.arraycopy) instead of merge. (Constructor of HLLCounter)
• Precompute harmonic mean in the HLLCSnapshot to avoid doing this on the fly. (getCountEstimate of HLLCounter)

UnitTest has add cost duration compare.

[asfgit]

Can one of the admins verify this patch?

[hit-lacus]

Local CI pass.

[coveralls]

Pull Request Test Coverage Report for Build 3850

• 16 of 16 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 23.643%

---

Totals
Change from base Build 3845:	0.02%
Covered Lines:	16835
Relevant Lines:	71206

---

💛 - Coveralls

[shaofengshi]

LGTM