Add linkClass() and addLinkClass() methods to pagination widgets

[vjik]

Q	A
Is bugfix?	❌
New feature?	✔️
Breaks BC?	❌

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 20 lines in your changes missing coverage. Please review.

Project coverage is 84.12%. Comparing base (9f88f51) to head (94c123c).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Pagination/KeysetPagination.php	0.00%	9 Missing ⚠️
src/Pagination/OffsetPagination.php	0.00%	9 Missing ⚠️
config/widgets-themes.php	0.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #274      +/-   ##
============================================
- Coverage     84.83%   84.12%   -0.71%     
- Complexity      629      633       +4     
============================================
  Files            50       50              
  Lines          2136     2154      +18     
============================================
  Hits           1812     1812              
- Misses          324      342      +18     

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