Implement Text Field Boxes

[traviskaufman]

Note: This does not cover the new UX interaction states for text fields in general. That is covered by a separate issue.

• Add a mdc-textfield--box class which provides the boxed background for a textfield, and alters any baselines that need to be alter
• Implement the ripple treatments for text field boxes.
• Ensure text field box dark mode treatments are in place
• Ensure dense mode treatments are in place
• Ensure text field boxes work within an RTL context
• Ensure text field box can gracefully degrade