BUG: Get font information more reliably when removing text

[samuelbradshaw]

Last month I contributed pull request #3216, an enhancement to PdfWriter.removeText() that allows users to remove only the specified fonts. Since then, I've come across a few PDFs where my simple logic to find fonts wasn't working. This fix walks through the PDF structure to find font references more reliably. I also added a few explanatory comments.

[codecov]

Codecov Report

Attention: Patch coverage is 96.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 96.59%. Comparing base (96ba79c) to head (d8bce21).

Files with missing lines	Patch %	Lines
pypdf/_writer.py	96.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3252      +/-   ##
==========================================
- Coverage   96.59%   96.59%   -0.01%     
==========================================
  Files          53       53              
  Lines        8957     8976      +19     
  Branches     1648     1658      +10     
==========================================
+ Hits         8652     8670      +18     
  Misses        183      183              
- Partials      122      123       +1     

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