[css-overflow] Initial value of `block-ellipsis`

[andreubotella]

As mentioned in the discussion, block-ellipsis currently defaults to none. This means that if you set continue: collapse explicitly, rather than using the (-webkit-)line-clamp shorthands, then by default wouldn't get an ellipsis.

With this change, should we make the initial value no-ellipsis, or change to auto? For continue: collapse, it probably makes a lot more sense to change it.

However, none was made the initial value when line-clamp was using continue: discard by default, and I think it might have been set like that because if in the future other region breaks are defined other than for line clamping, they maybe shouldn't have an ellipsis automatically applied. But currently continue: discard is the only use of region breaks, and that's not even the value of continue that line-clamp is setting anymore.

Given that, should we change the initial value to auto?

Originally posted by @andreubotella in #12416

[frivoal]

I think that if authors want an ellipsis by default, they should use line-clamp, not just continue, so I would prefer to keep the default as it is.
Then again, this is a very weakly held preference.