Instead of having a dedicated module for all-things dark mode related,
this commit moves the (S)CSS files into their respecting modules and
uses `web` and `web_enterprise` to provide the base infrastructure for
the dark mode (cf. dedicated assets bundle).
Note:
Don't forget that you have to handle 2 cases:
1: SCSS variables must be placed BEFORE bright ones
2: CSS variables must be placed AFTER
task-2710677
Part-of: odoo/odoo#102868
Pierre Paridans
dd9877e080