[css-text-3] replaced elements and atomic inlines with non default line-break

[frivoal]

This is a follow up to #4576

This makes replaced elements and atomic inlines with non default values for line-break behave the same as characters with line-breaking class ID for line breaking purposes. This gives the expected behavior for images used as “gaiji” and as emoji.

This cannot be the default behavior for compat reasons, but having it as an opt-in based on the rarely used line-break property should be safe, and opens up for further tweaking of the line breaking behavior via the usual set of properties.

[kojiishi]

I would like us to use any other properties than line-break for this purpose.

The effect of using incorrect values of line-break is visible only to some scripts. It is possible for authors to misunderstand and apply, for instance:

html { line-break: strict; }

but authors will not notice it has undesired side effects until they test it with CJK content. This can lead to a situation where global sites to use undesired typography only for CJK content.

/cc @r12a @himorin

[fantasai]

@kojiishi The initial value of line-break right now is auto, so non-CJK sites can use line-break: normal to make the change in behavior. Also I think, it's easy to say "put it on the image", img { line-break: normal; }, then it won't affect any other characters. Maybe we can make this an example so it's clearer.

[frivoal]

@fantasai, added an example: 34c697b. Feedback welcome.

[frivoal]

Closed as the resolution in #4949 (comment) decided on a different approach.