[system] Add missing TypeScript types for flexbox and shadows (#15781)
[system] Add missing TypeScript types for flexbox and shadows (#15781)

* Add missing style functions for display, flexbox, positions and shadows

* Add missing semicolons

* Fix typescript test

* Restore TS

rscnt/material-ui,oliviertassinari/material-ui,oliviertassinari/material-ui,oliviertassinari/material-ui,mbrookes/material-ui,mui-org/material-ui,rscnt/material-ui,callemall/material-ui,callemall/material-ui,mui-org/material-ui,kybarg/material-ui,callemall/material-ui,callemall/material-ui,allanalexandre/material-ui,rscnt/material-ui,kybarg/material-ui,mui-org/material-ui,mbrookes/material-ui,mbrookes/material-ui,lgollut/material-ui,kybarg/material-ui,kybarg/material-ui