feat(list): Updated two-line list to use typography baseline to match spec.

[abhiomkar]

BREAKING CHANGE

Fixes #3038

[lynnmercier]

This is related to #3083 ...but I didn't realize our mdc-list-item__secondary-text is inside our mdc-list-item__text. Why do we do that??

Can we have change our list HTML structure to be:

<li class="mdc-list-item">
  <span class="mdc-list-item__text">
    First-line text
  </span>
  <span class="mdc-list-item__secondary-text">
    Second-line text
  </span>
</li>

That would be more logical right?

or maybe we need another element, to separate the graphic from the two lines of text

<li class="mdc-list-item">
  <span class="mdc-list-item__graphic">
    <i class="material-icons">folder</i>
  </span>
  <div class="mdc-list-item__body">
    <span class="mdc-list-item__text">
      First-line text
    </span>
    <span class="mdc-list-item__secondary-text">
      Second-line text
    </span>
  </div>
</li>

[lynnmercier]

if the dense version is the same as the regular version...then you probably dont need it?

[codecov-io]

Codecov Report

Merging #3085 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3085   +/-   ##
=======================================
  Coverage   98.13%   98.13%           
=======================================
  Files         101      101           
  Lines        4444     4444           
  Branches      585      585           
=======================================
  Hits         4361     4361           
  Misses         83       83

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Screenshot test report

Commit 25b6419 vs. master:

• https://storage.googleapis.com/mdc-web-screenshot-tests/travis/2018/07/25/16_16_55_412/report/report.html

No diffs! 💯🎉

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Screenshot test report

Commit 628769f vs. master:

• https://storage.googleapis.com/mdc-web-screenshot-tests/travis/2018/07/25/16_33_35_588/report/report.html

No diffs! 💯🎉