Ensure bokeh correctly detects whether HTML/Markdown contains latex

[philippjfr]

Fixes #3429

[codecov]

Codecov Report

Merging #3438 (0e2c05b) into master (325f471) will decrease coverage by 0.00%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #3438      +/-   ##
==========================================
- Coverage   82.93%   82.92%   -0.01%     
==========================================
  Files         198      198              
  Lines       27017    27018       +1     
==========================================
- Hits        22407    22406       -1     
- Misses       4610     4612       +2     

Impacted Files	Coverage Δ
panel/config.py	58.75% <0.00%> (-0.17%)	⬇️
panel/models/markup.py	100.00% <100.00%> (ø)
panel/io/state.py	69.08% <0.00%> (-0.25%)	⬇️

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[philippjfr]

@MarcSkovMadsen So the fast templates have this bit of CSS in them:

  :not(:defined) {
    visibility: hidden;
  }

This seems to hide the mjx-container tags that MathJax adds to the page to render the LaTeX output. Do you recall why this rule had to be added?

[MarcSkovMadsen]

Yes. The fast documentation specifiks they should be added to avoid having the page look weird until web components have been defined and can be rendered correctly.

[philippjfr]

So it should be removed after the page is fully rendered?

[philippjfr]

Will merge and fix the fast template issue separately.