What problem does this solve or what need does it fill?

This allows for rotated layouts where the inline axis is vertical rather than horizontal, which is mainlly useful when the text contained within the layout is also vertical.

What solution would you like?

• Add WritingMode style
• Add support to the test generator for generating this style
• Add support for Flexbox algorithm
• Add support for CSS Grid algorithm
• Add support for Block algorithm
• Consider rethinking our caching scheme to be "inline centric"

We will need to implement to "rules for orthogonal flows" from the CSS specifications.

Additional context

writing-mode is also heavily used in WPT tests (especially CSS Grid tests). So we need support if want to pass those tests.