fix(textfield): change root element to <label>

[asyncLiz]

BREAKING CHANGE: text field's root element has changed from a <div> to a <label>

[asyncLiz]

I apologize in advance to whomever has to review this... 😅

[mdc-web-bot]

All 728 screenshot tests passed for commit 38e4f6c vs. master! 💯🎉

[mdc-web-bot]

All 728 screenshot tests passed for commit bcf3b85 vs. master! 💯🎉

[mdc-web-bot]

All 728 screenshot tests passed for commit 32a5a95 vs. master! 💯🎉

[mdc-web-bot]

All 728 screenshot tests passed for commit 5c83e3e vs. master! 💯🎉

[codecov-io]

Codecov Report

Merging #5383 into master will increase coverage by 0.4%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #5383     +/-   ##
=========================================
+ Coverage   97.22%   97.63%   +0.4%     
=========================================
  Files         164      163      -1     
  Lines        6267     6294     +27     
  Branches      834      857     +23     
=========================================
+ Hits         6093     6145     +52     
+ Misses        174      149     -25

Impacted Files	Coverage Δ
packages/mdc-textfield/icon/foundation.ts	98% <100%> (+0.17%)	⬆️
packages/mdc-chips/chip-set/component.ts	25.67% <0%> (-72.98%)	⬇️
packages/mdc-radio/foundation.ts	86.36% <0%> (-13.64%)	⬇️
packages/mdc-tab/foundation.ts	98.07% <0%> (-1.93%)	⬇️
testing/helpers/foundation.ts	87.23% <0%> (-1.23%)	⬇️
packages/mdc-tab-bar/foundation.ts	98.89% <0%> (-1.11%)	⬇️
packages/mdc-menu/foundation.ts	95.55% <0%> (-1.04%)	⬇️
packages/mdc-menu-surface/foundation.ts	99.12% <0%> (-0.88%)	⬇️
packages/mdc-list/foundation.ts	98.82% <0%> (-0.78%)	⬇️
packages/mdc-switch/component.ts	91.37% <0%> (-0.15%)	⬇️
... and 23 more

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[mdc-web-bot]

All 728 screenshot tests passed for commit 6a2d0b0 vs. master! 💯🎉

[mdc-web-bot]

All 602 screenshot tests passed for commit b4e9f4b vs. master! 💯🎉

[mdc-web-bot]

All 602 screenshot tests passed for commit f6db7e7 vs. master! 💯🎉

[mdc-web-bot]

All 602 screenshot tests passed for commit 79fe1a4 vs. master! 💯🎉

[asyncLiz]

Closing this PR in favor of #5439. Going to try syncing from internal to see if a new one stays happily ever after with my CL.