Initial work for Mpdf v7 compatibility

[jakejackson1]

No description provided.

[codecov]

Codecov Report

Merging #787 into development will decrease coverage by 0.28%.
The diff coverage is 38.02%.

@@               Coverage Diff               @@
##           development     #787      +/-   ##
===============================================
- Coverage        63.31%   63.02%   -0.29%     
===============================================
  Files              196      196              
  Lines            10311    10356      +45     
  Branches           215      215              
===============================================
- Hits              6528     6527       -1     
- Misses            3783     3829      +46

Impacted Files	Coverage Δ
pdf.php	80.24% <ø> (ø)	⬆️
src/controller/Controller_PDF.php	92.3% <ø> (-0.17%)	⬇️
src/deprecated.php	15.07% <0%> (-4.23%)	⬇️
src/view/View_PDF.php	79.16% <100%> (ø)	⬆️
src/model/Model_PDF.php	93.18% <100%> (-1.12%)	⬇️
src/statics/Queue_Callbacks.php	56.66% <100%> (+1.49%)	⬆️
src/helper/Helper_PDF.php	58.47% <68.75%> (+0.46%)	⬆️
src/controller/Controller_Settings.php	79.77% <0%> (+0.22%)	⬆️
api.php	93.8% <0%> (+0.52%)	⬆️

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