MDC Textfield prefix and suffix do not turn gray to match disabled state

[wagnermaciel]

Bug report

The MDC Textfield does not gray out the prefix and suffix text / icon when the MDC textfield is disabled.

Steps to reproduce

I tried to create a stackblitz using the demo html from material.io but could not get the prefix & suffix to be styled correctly

https://stackblitz.com/edit/mdc-textfield-demo-q442iq?file=index.html,index.js,index.scss

The steps to reproduce would be:

1. Create an MDC TextField with a prefix and suffix
2. Disable the text field.

Actual behavior

The prefix and suffix do not get grayed out.

Expected behavior

The prefix and suffix are grayed out.