CIF-2279 - Improve accessibility of carousel components

[herzog31]

Description

• Removed invalid aria roles.
• Changed button positioning (in DOM only), so that both buttons are in tab order before the cards.
• Added title and aria-label to buttons.
• Updated CSS to includes styles to differentiate between disabled and focused (via keyboard only) states of the buttons.
• Updated markup in unit test.

How Has This Been Tested?

• Manually tested by using the components via keyboard only.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes and the overall coverage did not decrease.
• All unit tests pass on CircleCi.
• I ran all tests locally and they pass.

[codecov]

Codecov Report

Merging #666 (e4231fc) into master (99972f6) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #666   +/-   ##
=========================================
  Coverage     88.44%   88.44%           
  Complexity     1598     1598           
=========================================
  Files           280      280           
  Lines          6986     6986           
  Branches       1047     1047           
=========================================
  Hits           6179     6179           
  Misses          610      610           
  Partials        197      197           

Flag	Coverage Δ
integration	59.56% <ø> (ø)
jest	85.61% <ø> (ø)
karma	89.06% <ø> (ø)
unittests	89.02% <ø> (ø)

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