Unify css files and move vendors assets to assets folder

[jordisala1991]

Subject

I am targeting this branch, because this is BC break.

Part of #7049

Requires #7081

Changelog

### Changed
- Unify css files into a single `app.css` file
- Move remaining third party assets from `src/Resources/public` to `assets` directory. Only necessary assets are exposed to the `public` dir

[SonataCI]

Could you please rebase your PR and fix merge conflicts?

[jordisala1991]

Let's wait a little bit, have to test this one further

[VincentLanglet]

Let's wait a little bit, have to test this one further

Do you use a SonataAdmin project to test this PR (and the previous) in order to check the css still works ?
I wonder if we could have some functional test for this ? With panther for example. cc @franmomu

[jordisala1991]

I was testing the previous PR, but with this one I discovered an unrelated bug #7085 .

Also with this PR some styles broke, so probably I am missing something. Just want to make sure the styles looks the same.

[jordisala1991]

Resolved the problems, my mistake importing files.

[VincentLanglet]

Do you prefer to fix #7087 before a merge ?

[jordisala1991]

There are two issues there: the first one I dont know yet how to fix, have to take a look, the second one is because I need to use the full version of select2. Anyway both issues are related to select2 js. Not related to this Pr.

[phansys]

Don't we need an upgrade note for these changes?
Regarding the changelog messages:
About the term "vendor", I think we must remove the backticks if we are using it in a colloquial way, otherwise we should specify if we are referencing a directory name or something else.
About the term "folder", my advice is to replace it with "dir" or "directory", since the folder concept is just a graphical representation for the real filesystem structure, called directory.

[jordisala1991]

Don't we need an upgrade note for these changes?

Regarding the changelog messages:

About the term "vendor", I think we must remove the backticks if we are using it in a colloquial way, otherwise we should specify if we are referencing a directory name or something else.

About the term "folder", my advice is to replace it with "dir" or "directory", since the folder concept is just a graphical representation for the real filesystem structure, called directory.

👍 applied the changes to the changelog.

About the upgrade note, I think we wrote one on the first PR warning about the fact that we are restricting what we show on the public folder. I think still applies the same. wdyt?

[phansys]

About the upgrade note, I think we wrote one on the first PR warning about the fact that we are restricting what we show on the public folder. I think still applies the same. wdyt?

If the upgrade notes for these changes are already covered in a previous PR, it's fine for me.

[VincentLanglet]

Thanks @jordisala1991