[css-logical] Add some logical version for CSS gradients

[nico3333fr]

Spec: https://drafts.csswg.org/css-logical/

We need a logical version for CSS gradients.

Use case

In ProtonMail, we are using a gradient to manage upload progress for attachments, here an example in Farsi (RTL)

Actually, we have to detect if user is using a RTL language, and adapt the

Solution

Either logical keyword or something like:

linear-gradient(to inline-end,...
linear-gradient(to inline-start,...
linear-gradient(to block-start,...
linear-gradient(to block-end,... 

Thanks :)

[Loirooriol]

Duplicate of #1724