fix(text-field): Should apply fullwidth modifier (#1582)

Author: trimox

packages/textfield/textarea.ts

@@ -15,6 +15,7 @@ import { MdcTextField } from './text-field';
     'class': 'mdc-text-field',
     '[class.mdc-text-field--textarea]': 'true',
     '[class.mdc-text-field--dense]': 'dense',
+    '[class.mdc-text-field--fullwidth]': 'fullwidth',
     '[class.mdc-text-field--invalid]': 'errorState'
   },
   template: `