[Feature request] Text directions like CSS writing-mode

** Is your feature request related to a problem? Please describe. **
I am trying to develop a GUI with top-to-bottom text, including North Asian and East Asian languages (Chinese, Japanese, Korean, Mongolian, Manchu, etc.).

** Describe the solution you'd like **
Able to set the text direction with one attribute.

** Describe alternatives you've considered **
Rotate the text for Mongolian, Manchu; rotate every character and then rotate the text for Chinese, Japanese, Korean.

** Additional context **
[Styling vertical Chinese, Japanese, Korean and Mongolian text](https://www.w3.org/International/articles/vertical-text/)

Start by reviewing Toga's existing text-widget APIs and platform backends, then compare the requested behavior with the linked W3C vertical-text guidance. Define how one attribute should express top-to-bottom and related writing modes across supported platforms; done means the behavior is implemented consistently for the stated language use cases and covered by tests.

Written by the indexing model from the issue text.