Images flowing within TextColumns

[gmischler]

Checklist:

• The GitHub pipeline is OK (green),
  meaning that both pylint (static code analyzer) and black (code formatter) are happy with the changes of this PR.
• A unit test is covering the code added / modified by this PR
• This PR is ready to be merged
• In case of a new feature, docstrings have been added, with also some documentation in the docs/ folder
• A mention of the change is present in CHANGELOG.md

This makes it possible to convert table cells to text region as the next step.

It might be worth considering if a FORM_FEED character in the text should trigger a page break in the traditional multi-line text methods.

By submitting this pull request, I confirm that my contribution is made under the terms of the GNU LGPL 3.0 license.

[codecov-commenter]

Codecov Report

Attention: 17 lines in your changes are missing coverage. Please review.

Comparison is base (40d64d4) 93.70% compared to head (27f4ee0) 93.79%.

❗ Current head 27f4ee0 differs from pull request most recent head d47fbd9. Consider uploading reports for the commit d47fbd9 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #973      +/-   ##
==========================================
+ Coverage   93.70%   93.79%   +0.08%     
==========================================
  Files          28       28              
  Lines        8276     8391     +115     
  Branches     1514     1544      +30     
==========================================
+ Hits         7755     7870     +115     
+ Misses        324      323       -1     
- Partials      197      198       +1     

Files	Coverage Δ
fpdf/line_break.py	99.14% <100.00%> (+<0.01%)	⬆️
fpdf/image_parsing.py	84.70% <90.32%> (+0.66%)	⬆️
fpdf/fpdf.py	93.04% <91.04%> (+0.29%)	⬆️
fpdf/text_region.py	93.55% <92.85%> (+0.96%)	⬆️

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[Lucas-C]

Really good job on this! 👍👍

After that PR, we will be very close to using TextRegions in table.py!