Set initial array list size

[justin-tay]

Sets the initial size of the ArrayList to the expected size when known.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 77.77778% with 4 lines in your changes missing coverage. Please review.

Project coverage is 78.65%. Comparing base (48ca3c2) to head (003f95d).
Report is 25 commits behind head on master.

Files	Patch %	Lines
.../java/com/networknt/schema/UnionTypeValidator.java	50.00%	0 Missing and 2 partials ⚠️
...java/com/networknt/schema/NotAllowedValidator.java	66.66%	1 Missing ⚠️
...n/java/com/networknt/schema/RequiredValidator.java	50.00%	1 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1062      +/-   ##
============================================
- Coverage     78.90%   78.65%   -0.25%     
- Complexity     1965     2018      +53     
============================================
  Files           172      190      +18     
  Lines          6352     6536     +184     
  Branches       1255     1244      -11     
============================================
+ Hits           5012     5141     +129     
- Misses          867      923      +56     
+ Partials        473      472       -1     

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