Add FDF support for form fill rendering test

[adrg]

This change is 

[codecov]

Codecov Report

Merging #389 into development will decrease coverage by 0.03%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           development     #389      +/-   ##
===============================================
- Coverage        63.12%   63.08%   -0.04%     
===============================================
  Files              249      249              
  Lines            47251    47251              
===============================================
- Hits             29827    29809      -18     
+ Misses           16729    16727       -2     
- Partials           695      715      +20     

Impacted Files	Coverage Δ
internal/e2etest/utils.go	70.00% <0.00%> (-10.00%)	⬇️
internal/jbig2/decoder/huffman/fixed_size_table.go	63.15% <0.00%> (-5.27%)	⬇️
model/optimize/image_ppi.go	73.84% <0.00%> (-1.54%)	⬇️
model/optimize/optimizer.go	87.14% <0.00%> (-1.43%)	⬇️
model/sighandler/sighandler_pkcs7.go	60.91% <0.00%> (-1.15%)	⬇️
model/signature_handler.go	70.27% <0.00%> (-0.91%)	⬇️
...ternal/jbig2/document/segments/halftone-segment.go	74.88% <0.00%> (-0.90%)	⬇️
ps/parser.go	80.67% <0.00%> (-0.85%)	⬇️
internal/jbig2/bitmap/blit.go	80.83% <0.00%> (-0.84%)	⬇️
internal/imageutil/rgbtobw.go	39.37% <0.00%> (-0.79%)	⬇️
... and 55 more

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[gunnsth]

LGTM