[Documentation] Improve languages list page

Idea

It would be nice to enhance the page that list supported languages (https://pygments.org/languages/) to add the corresponding alias / keyword / CSS class.

Resources

The template to modify:

https://github.com/pygments/pygments/blob/7620ef295ee9ac3ad2723847bc6722b5beec248e/doc/_templates/languages.html#L10-L17

The mapping between the name and the aliases is already done here: https://github.com/pygments/pygments/blob/master/pygments/lexers/_mapping.py

Example of other syntax highlighters that is already doing that on their documentation:

• List: https://prismjs.com/#supported-languages
• Table: https://highlightjs.readthedocs.io/en/latest/supported-languages.html

Motivation

Some mapping are trivial but some others are non-intuitive or have many aliases. The page list the name of the languages supported but not the aliases which is the information users will need if they build a website using pygments (devs) or are just end users using a solution that use pygments. So having the mapping on the documentation and not only on the source code will be very helpful.

Start with doc/_templates/languages.html and compare its current output with pygments/lexers/_mapping.py, which contains the language-to-alias mapping. Update the languages documentation page to show each language's corresponding alias, keyword, or CSS class as requested, then verify the generated page presents this information clearly.