Fixes for gaps in the ELM visitor

[JPercival]

• Added architecture tests to ensure ElmVisitor followed the expected conventions
• Added random ELM graph generation to ensure all nodes are visited
• Renamed ElmBaseVisitor -> BaseElmVisitor to match conventions for abstract classes
• Removed code that was pass through to super class
• Fixed traversal bugs to ensure operands and arguments are visited correctly

[github-actions]

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[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (cf7c30a) 62.64% compared to head (5fd11a7) 62.70%.

Files	Patch %	Lines
...k/cql/elm/requirements/ElmRequirementsVisitor.java	84.90%	4 Missing and 4 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1308      +/-   ##
============================================
+ Coverage     62.64%   62.70%   +0.05%     
+ Complexity     6158     6079      -79     
============================================
  Files           466      466              
  Lines         25424    25308     -116     
  Branches       4703     4711       +8     
============================================
- Hits          15928    15869      -59     
+ Misses         7348     7288      -60     
- Partials       2148     2151       +3     

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