feat: improve performance

[ert78gb]

The performance of the control is good on i5 or i7 machine, but poor on lower devices. Example ARM. This version of the control is 3-6 times faster.

The rxjs solution is beautiful, but the map and filter functions run multiple times on the same collection. I minimalized the modifications, but the performance could be much better if more maps, filters, etc functions were merged.

Summary:

• optimize selected options calculation
• calculate the highlighted text and active flag when filter items
• merge keydown and keyup events of the container div
• merge keydown, 'keyupandinput` events of the input control

[codecov-io]

Codecov Report

Merging #119 into master will increase coverage by 0.26%. The diff coverage is 89.74%.

@@            Coverage Diff             @@
##           master     #119      +/-   ##
==========================================
+ Coverage    90.7%   90.96%   +0.26%     
==========================================
  Files          15       15              
  Lines         484      498      +14     
  Branches       73       80       +7     
==========================================
+ Hits          439      453      +14     
- Misses         20       21       +1     
+ Partials       25       24       -1

Impacted Files	Coverage Δ
src/app/lib/ngx-select/ngx-select.classes.ts	89.28% <100%> (ø)	:arrow_up:
src/app/lib/ngx-select/ngx-select.component.ts	89.94% <89.47%> (+0.4%)	:arrow_up:

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[optimistex]

@ert78gb Merged into the development! Install it: npm i ngx-select-ex@dev