Add IndexMethod class

[Tigrov]

Related PR

• Move index type constants to IndexType class db#920

Q	A
Is bugfix?	❌
New feature?	✔️
Breaks BC?	❌
Fixed issues

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.74%. Comparing base (45a4b12) to head (af5e660).

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #384   +/-   ##
=========================================
  Coverage     99.74%   99.74%           
  Complexity      255      255           
=========================================
  Files            28       28           
  Lines           794      794           
=========================================
  Hits            792      792           
  Misses            2        2           

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