fix(buttons): display correct NgModel value inside OnPush component

[maxokorokov]

In short, the problem is that ngModel updates to the real value in the resolved promise, so we have to force mark for check all radios/checkboxes. Otherwise parent component with OnPush will prevent it.

Fixes #2980

[codecov-io]

Codecov Report

Merging #3000 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3000      +/-   ##
==========================================
+ Coverage   92.26%   92.27%   +<.01%     
==========================================
  Files          91       91              
  Lines        2870     2873       +3     
  Branches      463      464       +1     
==========================================
+ Hits         2648     2651       +3     
  Misses        163      163              
  Partials       59       59

Flag	Coverage Δ
#e2e	60.04% <0%> (-0.07%)	⬇️
#unit	90.65% <100%> (ø)	⬆️

Impacted Files	Coverage Δ
src/buttons/checkbox.ts	100% <100%> (ø)	⬆️
src/buttons/radio.ts	95.08% <100%> (+0.16%)	⬆️

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[benouat]

LTGM. Please proceed with merge