Add is_IS locale

[paunovic-stefan]

Added Icelandic locale.

Separate PR created for rc-pagination component with the corresponding locale.
react-component/pagination#109

Separate PR created for rc-calendar component with the corresponding locale.
react-component/calendar#295

will this be added to the ant.design v2.13.x? as well as ant.design v3.0

[mention-bot]

@paunovic-stefan, thanks for your PR! By analyzing the history of the files in this pull request, we identified @afc163, @damiangreen and @corneyl to be potential reviewers.

[codecov]

Codecov Report

Merging #7561 into antd-3.0 will increase coverage by 0.03%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##           antd-3.0    #7561      +/-   ##
============================================
+ Coverage     86.03%   86.07%   +0.03%     
============================================
  Files           252      256       +4     
  Lines          5256     5270      +14     
  Branches       1447     1450       +3     
============================================
+ Hits           4522     4536      +14     
  Misses          734      734

Impacted Files	Coverage Δ
components/locale-provider/is_IS.tsx	100% <100%> (ø)
components/calendar/locale/is_IS.tsx	100% <100%> (ø)
components/time-picker/locale/is_IS.tsx	100% <100%> (ø)
components/date-picker/locale/is_IS.tsx	100% <100%> (ø)

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