feat(notched-outline): Change notched outline to use 3 divs

[trimox]

As per material-components/material-components-web#4035

[codecov]

Codecov Report

Merging #1581 into master will increase coverage by 0.13%.
The diff coverage is 86.04%.

@@            Coverage Diff            @@
##           master   #1581      +/-   ##
=========================================
+ Coverage   89.66%   89.8%   +0.13%     
=========================================
  Files          98      98              
  Lines        3765    3766       +1     
  Branches      472     474       +2     
=========================================
+ Hits         3376    3382       +6     
+ Misses        218     213       -5     
  Partials      171     171

Impacted Files	Coverage Δ
packages/textfield/textarea.ts	100% <ø> (ø)	⬆️
packages/notched-outline/notched-outline-module.ts	100% <ø> (ø)	⬆️
packages/floating-label/floating-label.ts	93.33% <100%> (ø)	⬆️
packages/notched-outline/notched-outline.ts	100% <100%> (+20%)	⬆️
packages/line-ripple/line-ripple.ts	90.62% <100%> (ø)	⬆️
packages/textfield/text-field.ts	90.75% <79.31%> (+0.58%)	⬆️

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