feat(grid): show gaps immediately on handle hover

[liady]

This PR shows the grid gap background:

1. when hovering the the grid gap handle, -or-
2. when hovering the gap itself for more than 1500ms. this is due to the fact that sometimes the gaps are pretty large, so the handle might get "lost" and it's not easy to find and hover it

• [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]]

#14023 Bundle Size — 62.54MiB (~+0.01%).

3e5a39b(current) vs 916e8b9 master#13980(baseline)

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

Bundle metrics   2 changes 1 regression

	Current #14023	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 #14023	Baseline #13980
JS	62.53MiB (~+0.01%)	62.52MiB
HTML	11.05KiB (-0.33%)	11.09KiB

Bundle analysis report Branch feat/show-gaps-on-handle Project dashboard

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