Grid cleanup

[ruggi]

Problem:

The grid controls need cleaning up in multiple places.

Fix:

1. As a followup to Remove TargetGridCell from grid move #6033, stop doing duplicate cell lookups in the controls mouse handler and instead rely on custom strategy state data about the target root cell
2. Only trigger the shadow animation when the root cell changes (direct consequence of point 1)
3. Fix duplicate keys for grid resize handlers inside flatMaps
4. Remove a duplicate cell targets component which was a consequence of the spike code merges
5. Use a helper for the grid cell targets instead of hardcoded gridcell- shenanigans

[github-actions]

Try me

[relativeci]

#13262 Bundle Size — 62.51MiB (~-0.01%).

628c286(current) vs 6339ece master#13256(baseline)

Warning

Bundle contains 51 duplicate packages – View duplicate packages

Bundle metrics   3 changes 1 improvement

	Current #13262	Baseline #13256
Initial JS	45.56MiB(~-0.01%)	45.56MiB
Initial CSS	0B	0B
Cache Invalidation	21.85%	21.6%
Chunks	30	30
Assets	33	33
Modules	4323(+0.02%)	4322
Duplicate Modules	524	524
Duplicate Code	31.74%	31.74%
Packages	450	450
Duplicate Packages	51	51

Bundle size by type   2 changes 2 improvements

	Current #13262	Baseline #13256
JS	62.5MiB (~-0.01%)	62.5MiB
HTML	11.16KiB (-0.33%)	11.2KiB

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