Remove "fake" feature sub-folders that make files harder to find.
Note: If there are too many files in the main folder now, a new split
that actually makes sense can be done at a later time: this would not
just be code move, but removing coupling between said feature and the
rest of the code.
Apply consistent structure, where the top level folder is a feature (or
core), and sub-folders are subdivision of the feature depending on
context (closely related to assets bundles).
```
- core
- common
- public
- web
- feature
- common
- public
- web
```
The opportunity is taken to reorganize the top of the files and imports:
- Always use absolute path in imports to be able to find all usages of a
file with a single search.
- Reorganize imports to group them by module, and to sort them
alphabetically by path/feature.
- Always use single asterisk (*) for `odoo-module`: less characters yay!
And double asterisk should be used for JSDoc comments, not for custom
instructions.
Part of task-3265211
closes odoo/odoo#124168
Related: odoo/enterprise#42121
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>