Clear the text layer container when cancelling rendering

[calixteman]

It fixes #21217.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.90%. Comparing base (a55cec4) to head (82f55e7).

Files with missing lines	Patch %	Lines
web/text_layer_builder.js	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21219      +/-   ##
==========================================
- Coverage   55.97%   55.90%   -0.07%     
==========================================
  Files         218      218              
  Lines       59033    59035       +2     
==========================================
- Hits        33041    33004      -37     
- Misses      25992    26031      +39     

Flag	Coverage Δ
fonttest	?
unittest	55.21% <0.00%> (-0.02%)	⬇️
unittestcli	55.69% <0.00%> (-0.04%)	⬇️

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[timvandermeij]

I have confirmed locally that this fixes the root cause of the mentioned test in the issue as well as the ~10 other tests in the reorganize pages suite that also failed if this delay was introduced. Really great that this is fixed now; thank you!