This used to use doxygen's html blocks, which don't have a *direct*
equivalent in sphinx in code blocks.
Instead of adding this to the pygments highlighter, let's just use
some roles.
It's a teensy bit awkward as we then use block styling, but we want to
add more of our own styling anyway, so we can presumably get this
somehow, and these html tags look awkward and confuse people.
Fix#6640
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This displays a colored prompt, which we emulate by adding explicit
roles that are translated to css classes.
For other things, like "eror" this might not be enough because those
often need the rest of the line to still be styled, and I've not found
a way to add some explicit styling to a code block.
See #5696.
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