feat: added scrim tokens

[agliga]

Fixes #2042

• This PR contains CSS changes
• This PR does not contain CSS changes

Description

• Added scrim tokens

Screenshots

Checklist

• I verify the build is in a non-broken state
• I verify all changes are within scope of the linked issue
• I regenerated all CSS files under dist folder
• I tested the UI in all supported browsers
• I did a visual regression check of the components impacted by doing a Percy build and approved the build
• I tested the UI in dark mode and RTL mode
• I added/updated/removed Storybook coverage as appropriate

[LuLaValva]

Looks good on my end

[ianmcburnie]

Are we not using these tokens in our own Skin code anywhere? It would be good to switch out the current LESS variables and verify that the tokens work.

In dialog for example, I remember we needed "on/show" and "off/hide" variables to make things work:

https://github.com/eBay/skin/blob/master/src/less/mixins/private/dialog-mixins.less#L3

[ArtBlue]

Ok, replaced the LESS vars with CSS props and verified things look good.