feat(calendar): use nb-icon in navigation buttons

[yggg]

Please read and mark the following check list before creating a pull request:

• I read and followed the CONTRIBUTING.md guide.
• I read and followed the New Feature Checklist guide.

Short description of what this resolves:

Use button with icons for months navigation.
Also fixes #1355.

[codecov]

Codecov Report

Merging #1388 into next will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##             next    #1388      +/-   ##
==========================================
+ Coverage   82.58%   82.61%   +0.02%     
==========================================
  Files         237      237              
  Lines        7281     7282       +1     
  Branches      637      637              
==========================================
+ Hits         6013     6016       +3     
+ Misses       1080     1079       -1     
+ Partials      188      187       -1

Impacted Files	Coverage Δ
...vigation/calendar-pageable-navigation.component.ts	92.3% <ø> (-7.7%)	⬇️
...eme/components/calendar-kit/calendar-kit.module.ts	100% <100%> (ø)	⬆️
...mework/theme/components/button/button.component.ts	91.86% <0%> (+3.48%)	⬆️