fix(list): Follow hrefs on keypresses on links

[kfranqueiro]

Fixes #3406.

I also tested this by cherry-picking it into the feat/navigation-drawer branch, adding a unique hash to one of the drawer links, and testing click vs. space/enter, and both work (and also emit click events).

I also fixed formatting of a few test names and Sublime Text automatically removed some trailing whitespace (how'd all that get in there).

BREAKING CHANGE: Adds a followHref adapter API.

[mdc-web-bot]

All 353 screenshot tests passed for commit 57d0230 vs. master! 💯🎉

[mdc-web-bot]

All 353 screenshot tests passed for commit eb17c32 vs. master! 💯🎉

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@e21eee3). Click here to learn what that means.
The diff coverage is 100%.

@@            Coverage Diff            @@
##             master    #3407   +/-   ##
=========================================
  Coverage          ?   98.41%           
=========================================
  Files             ?      123           
  Lines             ?     5183           
  Branches          ?      638           
=========================================
  Hits              ?     5101           
  Misses            ?       82           
  Partials          ?        0

Impacted Files	Coverage Δ
packages/mdc-list/foundation.js	100% <100%> (ø)
packages/mdc-list/index.js	100% <100%> (ø)

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[williamernest]

LGTM

[abhiomkar]

LGTM.