perf: prefer .forEach over for...in and for...of

[ghiscoding]

• as per this article Measuring Performance of Different JavaScript Loop Types, the for...in and for...of aren't the most optimized for loops, the for and .forEach are more the most optimized methods across all browser engine and the for...in seems to be the worst to use and should be avoided when dealing with large dataset which can often be the case with this project

[codecov]

Codecov Report

Attention: 47 lines in your changes are missing coverage. Please review.

Comparison is base (f6dc75c) 88.0% compared to head (3ce8419) 88.0%.

Files	Patch %	Lines
packages/common/src/core/slickGrid.ts	21.3%	37 Missing ⚠️
packages/common/src/core/slickDataview.ts	0.0%	10 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1281     +/-   ##
========================================
- Coverage    88.0%   88.0%   -0.0%     
========================================
  Files         198     198             
  Lines       21350   21361     +11     
  Branches     7099    7109     +10     
========================================
+ Hits        18786   18791      +5     
- Misses       2564    2570      +6     

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