Minor improvements to astbuilder

[theunrepentantgeek]

What this PR does / why we need it:

Pulls in some improvements to the astbuilder package.

Harvested from PR #1533

How does this PR make you feel:

[codecov-commenter]

Codecov Report

Merging #1613 (0dffff5) into master (2578fbe) will decrease coverage by 0.01%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master    #1613      +/-   ##
==========================================
- Coverage   62.91%   62.90%   -0.02%     
==========================================
  Files         187      187              
  Lines       12355    12362       +7     
==========================================
+ Hits         7773     7776       +3     
- Misses       3898     3902       +4     
  Partials      684      684              

Impacted Files	Coverage Δ
hack/generator/pkg/astbuilder/builder.go	84.69% <80.95%> (-1.67%)	⬇️
hack/generator/pkg/astbuilder/calls.go	89.47% <100.00%> (ø)

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