Handle multibyte entries in CMaps.

[peterwilliams97]

Hi Gus,

This is only to show you how I am staring the multibyte CMap entry handling.

Please read the comments in the diff.

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This change is 

[codecov[bot]]

Codecov Report

Merging #353 into development will decrease coverage by 3.84%. The diff coverage is 82.05%.

@@               Coverage Diff               @@
##           development     #353      +/-   ##
===============================================
- Coverage        56.52%   52.67%   -3.85%     
===============================================
  Files              236      236              
  Lines            45792    45825      +33     
===============================================
- Hits             25882    24137    -1745     
- Misses           16572    18579    +2007     
+ Partials          3338     3109     -229     

Impacted Files	Coverage Δ
internal/textencoding/glyphs_glyphlist.go	86.66% <ø> (-3.34%)	:arrow_down:
internal/textencoding/cmap.go	28.00% <12.50%> (-16.69%)	:arrow_down:
model/font.go	51.97% <75.00%> (-5.47%)	:arrow_down:
extractor/text.go	47.59% <77.77%> (-16.05%)	:arrow_down:
internal/cmap/cmap_parser.go	53.82% <90.90%> (+0.12%)	:arrow_up:
internal/cmap/cmap.go	79.92% <97.29%> (+0.80%)	:arrow_up:
common/logging.go	31.70% <100.00%> (ø)
internal/jbig2/globals.go	0.00% <0.00%> (-100.00%)	:arrow_down:
internal/e2etest/memory_measure.go	0.00% <0.00%> (-100.00%)	:arrow_down:
internal/jbig2/decode.go	0.00% <0.00%> (-70.00%)	:arrow_down:
... and 54 more

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[peterwilliams97]

Saudi.pdf Test file for new test.