GROOVY-11559: fix addAllInterfaces for UnionTypeClassNode

[eric-milles]

In the multiple instanceof case, a UnionTypeClassNode is created. A call to addAllInterfaces triggers a call to parameterizeType with the union type as the hint and each of the instanceof types as the target. The walk type hierarchy should not be entered for a union type.

https://issues.apache.org/jira/browse/GROOVY-11559

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.8323%. Comparing base (9acdef1) to head (a247964).

Additional details and impacted files

@@                Coverage Diff                 @@
##               master      #2147        +/-   ##
==================================================
+ Coverage     68.8261%   68.8323%   +0.0062%     
- Complexity      29439      29445         +6     
==================================================
  Files            1420       1420                
  Lines          113162     113162                
  Branches        19549      19549                
==================================================
+ Hits            77885      77892         +7     
+ Misses          28739      28732         -7     
  Partials         6538       6538                

Files with missing lines	Coverage Δ
...a/org/codehaus/groovy/ast/tools/GenericsUtils.java	67.1548% <100.0000%> (ø)

... and 2 files with indirect coverage changes