[css-shapes-1] Optional values shouldn't be serialized

[mozilla-apprentice]

Resolutions were made for csswg-drafts/#8695.

[css-shapes-1] Optional values shouldn't be serialized

• RESOLVED: We fix the example and tests based on it
• RESOLVED: Remove the part about serializing calc expressions from Shapes spec

Discussion.

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To file a bug automatically for these resolutions, add the bug label to the issue.

If no bug is needed, the issue can be closed.

[BorisChiou]

https://bugzilla.mozilla.org/show_bug.cgi?id=1837340