Enhancement of merging algorithm.

[MaksimOrlov]

@dilipkrish , I added few unit tests, one integration test, fixed one bug, and made some performance enhancement.

[codecov]

Codecov Report

Merging #3298 into master will increase coverage by 0.07%.
The diff coverage is 99.21%.

@@             Coverage Diff              @@
##             master    #3298      +/-   ##
============================================
+ Coverage     92.89%   92.97%   +0.07%     
- Complexity     3525     3542      +17     
============================================
  Files           382      382              
  Lines          9358     9389      +31     
  Branches        776      760      -16     
============================================
+ Hits           8693     8729      +36     
+ Misses          476      468       -8     
- Partials        189      192       +3     

Impacted Files	Coverage Δ	Complexity Δ
...umentation/spring/web/scanners/ApiModelReader.java	95.82% <98.95%> (+0.64%)	102.00 <74.00> (+13.00)
...x/documentation/schema/ModelReferenceProvider.java	97.43% <100.00%> (ø)	15.00 <0.00> (ø)
.../documentation/schema/TypeNameIndexingAdapter.java	58.33% <100.00%> (+3.78%)	9.00 <1.00> (ø)
...ocumentation/spi/schema/contexts/ModelContext.java	87.23% <100.00%> (+0.56%)	32.00 <1.00> (ø)
...umentation/spring/web/scanners/MergingContext.java	100.00% <100.00%> (+4.65%)	20.00 <10.00> (+3.00)
...ation/spring/web/scanners/ComparisonCondition.java	62.50% <0.00%> (+6.25%)	6.00% <0.00%> (+1.00%)

[dilipkrish]

Thank @MaksimOrlov 🥳