fix(search): emit activate and deactivate events

[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:

Emit search activate and deactivate events when search opened from NbSearchComponent.

[codecov]

Codecov Report

Merging #1162 into master will decrease coverage by 0.01%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master    #1162      +/-   ##
==========================================
- Coverage   78.86%   78.84%   -0.02%     
==========================================
  Files         200      200              
  Lines        6066     6070       +4     
  Branches      469      469              
==========================================
+ Hits         4784     4786       +2     
- Misses       1167     1169       +2     
  Partials      115      115

Impacted Files	Coverage Δ
...mework/theme/components/search/search.component.ts	46.42% <50%> (+0.13%)	⬆️