New theme generation and filenaming with hashing should apply to dark mode style too

[cderv]

This is a follow up on 1.6 fix

• themes: use content hash in cache key and output file name #10611

The current solution does not apply to dark theme which builds to bootstrap-dark.min.css. No hash is used.

quarto create project website test-dark

Add to about.qmd this config

format:
  html:
    fontcolor: red

and this in _qaurto.yml

format:
  html:
    theme: 
      light: flatly
      dark: darkly

Then do quarto render

Light theme

This now works well. The red font color will only apply to about.html, and not the entire website

Dark theme

Switch to dark theme now with toggle. This still doesn't work and the configuration applies to whole website, like initial issue for light theme

• Different theme configuration for some page within a website does impact the whole website #10087

When looking at CSS files produced we see no hash is appended.

❯ ls .\_site\site_libs\bootstrap\

    Directory: C:\Users\chris\AppData\Local\Temp\quarto\test-subdir\_site\site_libs\bootstrap

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
-a---          17/09/2024    11:26         474885 bootstrap-cbee0a5f18ab906682e9d4fb633eabe1.min.css
-a---          17/09/2024    11:27         474541 bootstrap-dark.min.css
-a---          17/09/2024    11:27         474797 bootstrap-fcdf0d5c94eae0f74b37b7cfe1fba367.min.css
-a---          05/09/2024    15:43          98163 bootstrap-icons.css
-a---          17/09/2023    07:15         176200 bootstrap-icons.woff
-a---          05/09/2024    15:50          80668 bootstrap.min.js

We probably need to extend the initial fix to dark theming too, to have a boostrap-dark-<hash>.min.css.

@cscheid you may know how to do it quickly. Otherwise, I can take a shot at this based on #10611