Support for mask-border CSS shorthand property

[rcj-siteimprove]

Support for mask-border CSS shorthand property and its longhands.

Longhands:

• mask-border-source
• mask-border-slice
• mask-border-width
• mask-border-outset
• mask-border-repeat
• mask-border-mode

Shorthand:

• mask-border

[changeset-bot]

⚠️ No Changeset found

Latest commit: 7c378d8

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[rcj-siteimprove]

!pr extract

[rcj-siteimprove]

Since these are not supported anywhere yet, I am closing this.