[css-inline-3] Split text-line-edge from text-box-edge #8696

As I understand it, there was a conversation (mentioned in this comment) between @fantasai and WebKit’s zalan (not sure if there is a GitHub handle for them) around
splitting what is currently called text-box-edge into two properties - one that factors into line box sizing, and another that determines the text-box-trim metrics.

Apparently further conversation between zalan and @litherum resulted in this issue describing possible changes to line-height instead. But from the breakout session discussion I think the current idea is to have separate properties instead of adding more complications to line-height.

So I am filing this issue to have a place to discuss the property split.