refactor(pagination): simplify the way disabled links are handled

[maxokorokov]

Small refactoring after #3468 and #3471:

• ellipsis should always be disabled
• use prevDisabled() and nextDisabled() where possible

[codecov-io]

Codecov Report

Merging #3474 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3474   +/-   ##
=======================================
  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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