feat(timepicker): allow null value and change validation state on manual update

[valorkin]

fixes #2907

go to:
http://localhost:4200/#/timepicker#dynamic

1. clean button should clean timepicker value
2. manually time 12:aa (invalid time, should mark field as not valid)
   this is kinda dirty

@EvilAlexei please add timepicker validation to v2 roadmap

[codecov]

Codecov Report

Merging #3084 into development will decrease coverage by 0.01%.
The diff coverage is 33.33%.

@@               Coverage Diff               @@
##           development    #3084      +/-   ##
===============================================
- Coverage        65.54%   65.52%   -0.02%     
===============================================
  Files              209      209              
  Lines             5604     5607       +3     
  Branches           985      986       +1     
===============================================
+ Hits              3673     3674       +1     
- Misses            1669     1671       +2     
  Partials           262      262

Impacted Files	Coverage Δ
src/timepicker/timepicker.component.ts	91.74% <33.33%> (-1.66%)	⬇️

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[YevheniiaMazur]

Tested, looks good