Maintain Grid Cell Pins.

[seanparsons]

Problem:
When dragging around grid children, currently the pins are reset to top/left regardless of what pins are set on the element.

Fix:
The first part of this work was to re-use the existing logic for updating the pins from other strategies that do maintain the pins, using the containing block of the element to calculate the pins against. However, this uncovered a flaw in that approach in that the element may at the same time be moved to a different set of coordinates within the grid. This results in the containing block of the element changing, which means that for one frame (each time it changes) the element jumps as the pins were calculated against the old containing block and the coordinates are also changed.

The solution for this secondary problem was to create an analogous set of elements with the new coordinates and retrieve the containing block from those. Since this is only done once per frame the cost is very small and doesn't affect the performance of the operation.

Commit Details:

• Added printPinAsString utility function.
• Implemented getGridRelativeContainingBlock to calculate a new containing block by
  building a minimal purely HTML reproduction of the grid so as to use the browser
  logic for the position and size of the containing block.
• Refactored out getNewGridElementProps from the start of runGridChangeElementLocation
  so that it can be used to identify the new grid position on its own.
• Refactored out getMoveCommandsForDrag from getMoveCommandsForSelectedElement.
• Replaced gridChildAbsoluteMoveCommands with a call to getMoveCommandsForDrag
  in the Grid Absolute Move strategy.
• Added GridElementChildContainingBlockKey for simplicity.

Manual Tests:
I hereby swear that:

• I opened a hydrogen project and it loaded
• I could navigate to various routes in Play mode

[github-actions]

Try me

[relativeci]

#15341 Bundle Size — 58.2MiB (+0.01%).

9d94985(current) vs d1d46c1 master#15340(baseline)

Warning

Bundle contains 70 duplicate packages – View duplicate packages

Bundle metrics   3 changes 1 regression

	Current #15341	Baseline #15340
Initial JS	41.17MiB(+0.02%)	41.17MiB
Initial CSS	0B	0B
Cache Invalidation	18.23%	18.67%
Chunks	20	20
Assets	22	22
Modules	4189	4189
Duplicate Modules	213	213
Duplicate Code	27.24%(-0.04%)	27.25%
Packages	477	477
Duplicate Packages	70	70

Bundle size by type   2 changes 1 regression 1 improvement

	Current #15341	Baseline #15340
JS	58.19MiB (+0.01%)	58.19MiB
HTML	9.4KiB (-0.21%)	9.42KiB

Bundle analysis report Branch fix/maintain-grid-cell-pins Project dashboard

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