[SDK] Add base2 exponential histogram indexer

[euroelessar]

Updates #1391

Changes

Add Base2ExponentialHistogramIndexer for calculating index for a given value and scale.
It will be used in base2 exponential histogram in followup changes.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[marcalff]

LGTM, and well done.

[esigo]

LGTM
Thanks :)

[lalitb]

LGTM. Thanks

[codecov]

Codecov Report

Merging #2173 (cd45a94) into main (f5fd906) will increase coverage by 0.03%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2173      +/-   ##
==========================================
+ Coverage   87.48%   87.50%   +0.03%     
==========================================
  Files         168      169       +1     
  Lines        4869     4887      +18     
==========================================
+ Hits         4259     4276      +17     
- Misses        610      611       +1     

Impacted Files	Coverage Δ
...aggregation/base2_exponential_histogram_indexer.cc	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

[dufferzafar]

Is there a timeline/plan as to when the exponential histogram would be in usable shape?

@euroelessar Could you please specify the next steps one would need to take to implement this?

I've been going over the code and would like to take a stab at it.