fix(material/datepicker): range picker placeholders not hidden in high contrast mode
fix(material/datepicker): range picker placeholders not hidden in high contrast mode

Fixes that the placeholders were showing up behind the label in high contrast mode.

DevVersion/material2,crisbeto/material2,crisbeto/material2,crisbeto/material2,josephperrott/material2,mmalerba/material2,angular/components,DevVersion/material2,mmalerba/material2,crisbeto/material2,mmalerba/material2,angular/components,angular/components,DevVersion/material2,josephperrott/material2,josephperrott/material2,josephperrott/material2,DevVersion/material2,mmalerba/material2,josephperrott/material2,mmalerba/material2,DevVersion/material2,angular/components