refactor: Rename css custom properties with component name prefix & undo -default

[lukaskoeller]

Motivation

When @layer is implemented, there is no real reason for using a -default fallback in the css custom properties since styling conflicts are solved through that.
Furthermore, to make usage of higher up defined css custom properties in usage more clear, they should be prefixed with their component name.

Example

<fd-section>
    <fd-gallery style="--fd-gallery-gap: var(--fd-section-padding-inline)">
        ...
    </fd-gallery>
</fd-section>

Here, it is clear that I want to have the <fd-gallery> gap to always be the inline padding of <fd-section>.