fix: support strict template check

[yggg]

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

Short description of what this resolves:

Fixes #2263, Fixes #2247 and #2221 (comment)

BREAKING CHANGE:
Generic value type removed from NbSelectComponent

[codecov]

Codecov Report

Merging #2273 into master will decrease coverage by 0.09%.
The diff coverage is 79.16%.

@@            Coverage Diff             @@
##           master    #2273      +/-   ##
==========================================
- Coverage   81.65%   81.55%   -0.10%     
==========================================
  Files         244      244              
  Lines        7359     7369      +10     
  Branches      771      773       +2     
==========================================
+ Hits         6009     6010       +1     
- Misses       1122     1131       +9     
  Partials      228      228              

Impacted Files	Coverage Δ
...e/components/accordion/accordion-item.component.ts	30.95% <ø> (ø)
.../theme/components/accordion/accordion.component.ts	41.66% <ø> (ø)
...work/theme/components/actions/actions.component.ts	100.00% <ø> (ø)
...ramework/theme/components/alert/alert.component.ts	92.95% <ø> (ø)
...mework/theme/components/button/button.component.ts	87.05% <ø> (ø)
...calendar-day-picker/calendar-day-cell.component.ts	94.44% <ø> (ø)
...lendar-day-picker/calendar-day-picker.component.ts	100.00% <ø> (ø)
...lendar-days-names/calendar-days-names.component.ts	94.11% <ø> (ø)
...ndar-month-picker/calendar-month-cell.component.ts	93.75% <ø> (ø)
...ar-month-picker/calendar-month-picker.component.ts	83.87% <ø> (ø)
... and 44 more