fix(grid): dont generate gaps until the placeholder grid was updated

[liady]

Problem: Currently since we're relying on the grid metadata for row/column count and on the grid placeholder to get the actual cells, when adding a row/column to the grid via the inspector the metadata is updated before the grid DOM element, which causes a crash when trying to access a non-existing cell

Fix: Wait for the grid placeholder to be consistent with the metadata, otherwise return an empty gap array

• [X] I opened a hydrogen project and it loaded
• [X] I could navigate to various routes in Preview mode

[github-actions[bot]]

Try me

[relativeci[bot]]

#14019 Bundle Size — 62.54MiB (~+0.01%).

5d531aa(current) vs 916e8b9 master#13980(baseline)

[!WARNING] Bundle contains 70 duplicate packages – View duplicate packages

Bundle metrics   2 changes 1 regression

	Current #14019	Baseline #13980
Initial JS	45.67MiB(~+0.01%)	45.67MiB
Initial CSS	0B	0B
Cache Invalidation	21.63%	21.56%
Chunks	30	30
Assets	33	33
Modules	4377	4377
Duplicate Modules	519	519
Duplicate Code	31.63%	31.63%
Packages	472	472
Duplicate Packages	70	70

Bundle size by type   2 changes 1 regression 1 improvement

	Current #14019	Baseline #13980
JS	62.52MiB (~+0.01%)	62.52MiB
HTML	11.05KiB (-0.33%)	11.09KiB

Bundle analysis report Branch fix/inconsistent-cell-count Project dashboard

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