Intent to implement and ship: break-spaces value of the white-space property

[Violet L]

Summary: implement and ship value "break-spaces" of "white-space" CSS property

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1351432

Link to standard: https://drafts.csswg.org/css-text-3/#valdef-white-space-break-spaces

Platform coverage: all.

Estimated or target release: 69

Preference behind which this will be implemented: none.

Do other browser engines implement this?

Chrome has shipped this value in latest dev channel (76) https://bugs.chromium.org/p/chromium/issues/detail?id=767634

Safari Tech Preview 80
https://webkit.org/blog/8825/release-notes-for-safari-technology-preview-80/
https://trac.webkit.org/changeset/244036/webkit/

web-platform-tests: We have existing WPTs. In /css/css-text/white-space/

Is this feature restricted to secure contexts? No.