feat(slider): create a CDK slider component

It would be nice to have a CDK slider that allows for more user customization than `mat-slider`.

Things to support:
- Multiple thumbs (should follow a11y pattern here: http://oaa-accessibility.org/example/32/)
- Provides elements to style for things like thumb, filled track, non-filled track, etc, but leaves that styling up to the user
- Should be able to base `mat-slider` off of it

Start by reviewing the existing mat-slider and the linked accessibility pattern for the proposed CDK API. Done means a customizable slider supports multiple thumbs, exposes styleable thumb and track elements, and can serve as the basis for mat-slider.

Written by the indexing model from the issue text.