CSS flexbox properties missing on native

[necolas]

Describe the issue

Native is missing support for:

• justifyItems
• justifySelf
• placeContent (polyfillable)
• placeItems
• placeSelf

Upstream issue for Yoga facebook/yoga#1649

There might also be missing support for certain values for these and other flexbox properties

Expected behavior

Support for all of flexbox

Steps to reproduce

.

Test case

No response

Additional comments

No response

[NickGerleman]

There might also be missing support for certain values for these and other flexbox properties

A lot of the stuff that was added in the box alignment spec is missing at the moment. One that comes to mind are start and end keywords separate from flex-start/flex-end.