textfield mixins file uses imports included in the file

[TedSander]

What MDC Web Version are you using?

HEAD

What browser(s) is this bug affecting?

N/A

What OS are you using?

Linux

What are the steps to reproduce the bug?

Import mdc-textfiled/mixins without importing any other files from that directory.
Use mdc-text-field-outlined-dense_ or any of the other dense mixins

What is the expected behavior?

Scss file will compile without build error

What is the actual behavior?

Error not finding $mdc-text-field-box-dense-label-position-y which is in the variables import.