[#308] Fixed Layout masonry is not applied when nested Layout is used.

[AlexSkrypnyk]

closes #308

This PR changes 2 things:

1. We are no longer observing the grid's items - we are observing grid's items' children to track the change of their heigh.
2. The selection of the grid elements is now scoped to the immediate children to allow binding to nested layouts correctly.

22.mov

[codecov]

Codecov Report

Attention: Patch coverage is 8.33333% with 11 lines in your changes missing coverage. Please review.

Project coverage is 13.92%. Comparing base (9617c4a) to head (d26d7ca).

Files	Patch %	Lines
components/00-base/layout/layout.js	0.00%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #310      +/-   ##
==========================================
- Coverage   13.97%   13.92%   -0.05%     
==========================================
  Files          27       27              
  Lines        1281     1285       +4     
  Branches      306      306              
==========================================
  Hits          179      179              
- Misses        886      890       +4     
  Partials      216      216              

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