build: fix race condition when building styles (#15860)
build: fix race condition when building styles (#15860)

Fixes the build not waiting for the styles to finish building before starting to compile TS.
josephperrott/material2,Jefiozie/material2,angular/components,DevVersion/material2,jelbourn/material2,jelbourn/material2,jelbourn/material2,josephperrott/material2,crisbeto/material2,josephperrott/material2,angular/components,Jefiozie/material2,andrewseguin/material2,jelbourn/material2,crisbeto/material2,andrewseguin/material2,crisbeto/material2,mmalerba/material2,Jefiozie/material2,mmalerba/material2,andrewseguin/material2,angular/components,DevVersion/material2,DevVersion/material2,andrewseguin/material2,andrewseguin/material2,jelbourn/material2,Jefiozie/material2,mmalerba/material2,angular/components,mmalerba/material2,josephperrott/material2,josephperrott/material2,mmalerba/material2,Jefiozie/material2,DevVersion/material2,DevVersion/material2,crisbeto/material2