feat(pagination): aria-current attribute support

[peterblazejewicz]

This commit adds support for aria-current attribute as per:
https://getbootstrap.com/docs/4.3/components/pagination/#disabled-and-active-states
https://developer.mozilla.org/en-US/docs/Web/CSS/Layout_cookbook/Pagination

Thanks!

[maxokorokov]

LGTM, thanks!

Will merge when Travis is green

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By the way just found out while looking at examples that we're also missing aria-disabled attributes on <a> links → https://getbootstrap.com/docs/4.3/components/pagination/#disabled-and-active-states

If you're motivated :)

[codecov-io]

Codecov Report

Merging #3470 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3470   +/-   ##
=======================================
  Coverage   91.14%   91.14%           
=======================================
  Files          96       96           
  Lines        2800     2800           
  Branches      516      516           
=======================================
  Hits         2552     2552           
  Misses        190      190           
  Partials       58       58

Flag	Coverage Δ
#e2e	56.21% <ø> (ø)	⬆️
#unit	87.99% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
src/pagination/pagination.ts	100% <ø> (ø)	⬆️

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[ihorzenich]

@peterblazejewicz Keeping <span class="sr-only">(current)</span> together with aria-current="page" on parent cause double announcement of "current" page in NVDA screen-reader.

It is necessary to remove <span class="sr-only">(current)</span> from ngb-pagination: #3870