Browsers handle ideographic space differently during line-breaking

[r12a]

Browsers differ in how they handle line breaks for IDEOGRAPHIC SPACE (U+3000).

[r12a]

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[xfq]

• Issue for collecting requirements: https://github.com/w3c/clreq/issues/411
• Line_Break property: BA (tailorable)
• Spec issues: https://github.com/w3c/csswg-drafts/issues/6903
• Test case