Initial support for accessibility

[dontcallmedom]

While likely far from being complete, this pull request adds some initial support to make c3 charts more accessible:

• adding a few WAI ARIA annotations (on tooltips, lines, grid focus)
• making the charts keyboard navigable
• making tooltips more accessible

[codecov-io]

Codecov Report

Merging #2317 into master will decrease coverage by 1.02%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #2317      +/-   ##
==========================================
- Coverage   75.82%   74.79%   -1.03%     
==========================================
  Files          51       51              
  Lines        4227     4234       +7     
==========================================
- Hits         3205     3167      -38     
- Misses       1022     1067      +45     

Impacted Files	Coverage Δ
src/grid.js	75.00% <ø> (ø)
src/shape.line.js	70.69% <ø> (ø)
src/interaction.js	37.70% <11.11%> (-1.50%)	⬇️
src/core.js	89.33% <100.00%> (ø)
src/tooltip.js	81.37% <100.00%> (ø)
src/arc.js	73.68% <0.00%> (-12.29%)	⬇️
src/api.focus.js	91.42% <0.00%> (-8.58%)	⬇️

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[msftedad]

Hi Team,

Hi Team, is there any update on this bug?

[msftedad]

Hi Team,
Any update on this issue?

[msftedad]

Hi Team,
Any update on this issue?