feat(list): Add density mixin to list

[abhiomkar]

Description

• Added mdc-list-single-line-density() mixin to customize density of single line list variant.
• Fixed shape mixin to accept percentage radius value.
• Added additional screenshot tests (Two-line, shape etc).

BREAKING CHANGE: Renamed mixin mdc-list-item-shape-radius() => mdc-list-single-line-shape-radius()

Fixes #5046

[codecov-io]

Codecov Report

Merging #5069 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #5069   +/-   ##
========================================
  Coverage    98.68%   98.68%           
========================================
  Files          122      122           
  Lines         6009     6009           
  Branches       792      792           
========================================
  Hits          5930     5930           
  Misses          78       78           
  Partials         1        1

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[mdc-web-bot]

🤖 Beep boop!

Screenshot test report 🚦

15 screenshots changed from develop on commit 5ac09a7:

• https://storage.googleapis.com/mdc-web-screenshot-tests/travis/2019/09/11/18_55_39_672/report/report.html?utm_source=github&utm_medium=pr_comment

Details

15 Added:

• spec/mdc-list/classes/list-group.html

• spec/mdc-list/classes/two-line.html

• spec/mdc-list/mixins/density-checkbox.html

• spec/mdc-list/mixins/density.html

• spec/mdc-list/mixins/shape-single-line.html