Allow walking of schema for items keyword when non-array node is provided

[anjnerajat]

Resolves #785

Fixing ItemsValidator202012 walk flow.
Making UnevaluatedProperties CollectorContext's key public as was in 1.0.76.

[codecov-commenter]

Codecov Report

Merging #786 (b3efd56) into master (f09740a) will decrease coverage by 0.04%.
The diff coverage is 0.00%.

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@@             Coverage Diff              @@
##             master     #786      +/-   ##
============================================
- Coverage     74.87%   74.83%   -0.04%     
  Complexity     1191     1191              
============================================
  Files           122      122              
  Lines          4103     4105       +2     
  Branches        790      790              
============================================
  Hits           3072     3072              
- Misses          705      707       +2     
  Partials        326      326              

Impacted Files	Coverage Δ
...ava/com/networknt/schema/ItemsValidator202012.java	37.28% <0.00%> (-1.31%)	⬇️
...tworknt/schema/UnevaluatedPropertiesValidator.java	95.00% <ø> (ø)

[stevehu]

@anjnerajat Thanks for the quick fix.