Support justifyItems and justifySelf

[Nicolas Gallagher]

Report

• I have searched existing issues and this is not a duplicate

Issues and Steps to Reproduce

• CSS Flexbox properties justifyItems and justifySelf are not supported (e.g., in React Native).
• Also properties placeContent, placeItems, and placeSelf - which could be implemented once all the align* and justify* props are supported.
• Couldn't find any references to them via code search of the repo.

Expected Behavior

Support for the missing properties.

[Nick Gerleman]

justify-items and justify-self for flex containers is confined to absolutely positioned items, so it will be a bit less common than the usage for block, grid. Still potentially worth adding though (cc @joevilches who recently spent a lot of time fixing up absolutely positioned child alignment).

place-* shorthands seem sane enough to add, but probably at RN layer. I've been trying to get to a place where Yoga operates on something closer to computed style.