Freeze grid template during child move (#6201)

**Problem:**

Moving grid elements if the template is somewhat dynamic will result in
the grid elements likely jumping around because their template changes
constantly.

**Fix:**

Freeze the template during the interaction, by using the calculated
dimensions, and restore it once the interaction completes.

In the example below, one column is made `min-content` with some
fixed-sized elements inside.

| Before | After |
|-------|-------------|
| ![Kapture 2024-08-07 at 15 37
27](https://github.com/user-attachments/assets/da2d824a-ad02-494a-8ff6-7cc03e3b5c95)
| ![Kapture 2024-08-07 at 15 36
21](https://github.com/user-attachments/assets/283a5fc0-69b9-41e3-85d2-51be14279585)
|

Fixes #6200

editor/src/components/canvas/canvas-strategies/strategies/grid-rearrange-move-strategy.ts

@@ -1,5 +1,18 @@
+import type { ElementPath } from 'utopia-shared/src/types'
 import { MetadataUtils } from '../../../../core/model/element-metadata-utils'
 import * as EP from '../../../../core/shared/element-path'
+import type {
+  ElementInstanceMetadataMap,
+  GridAutoOrTemplateBase,
+} from '../../../../core/shared/element-template'
+import * as PP from '../../../../core/shared/property-path'
+import { printGridAutoOrTemplateBase } from '../../../inspector/common/css-utils'
+import type { PropertyToUpdate } from '../../commands/set-property-command'
+import {
+  propertyToDelete,
+  propertyToSet,
+  updateBulkProperties,
+} from '../../commands/set-property-command'
 import { GridControls } from '../../controls/grid-controls'
 import type { CanvasStrategyFactory } from '../canvas-strategies'
 import { onlyFitWhenDraggingThisControl } from '../canvas-strategies'
@@ -34,6 +47,13 @@ export const gridRearrangeMoveStrategy: CanvasStrategyFactory = (
     return null
   }
 
+  const gridPath = EP.parentPath(selectedElement)
+
+  const initialTemplates = getGridTemplates(canvasState.startingMetadata, gridPath)
+  if (initialTemplates == null) {
+    return null
+  }
+
   return {
     id: 'rearrange-grid-move-strategy',
     name: 'Rearrange Grid (Move)',
@@ -83,14 +103,98 @@ export const gridRearrangeMoveStrategy: CanvasStrategyFactory = (
         return emptyStrategyApplicationResult
       }
 
-      return strategyApplicationResult(moveCommands, {
-        grid: {
-          targetCell: targetGridCell,
-          draggingFromCell: draggingFromCell,
-          originalRootCell: originalRootCell,
-          currentRootCell: targetRootCell,
+      const midInteractionCommands = [
+        // during the interaction, freeze the template with the calculated values…
+        updateBulkProperties('mid-interaction', gridPath, [
+          propertyToSet(
+            PP.create('style', 'gridTemplateColumns'),
+            printGridAutoOrTemplateBase(initialTemplates.calculated.columns),
+          ),
+          propertyToSet(
+            PP.create('style', 'gridTemplateRows'),
+            printGridAutoOrTemplateBase(initialTemplates.calculated.rows),
+          ),
+        ]),
+      ]
+
+      const onCompleteCommands = [
+        // …eventually, restore the grid template on complete.
+        updateBulkProperties(
+          'on-complete',
+          gridPath,
+          restoreGridTemplateFromProps(initialTemplates.fromProps),
+        ),
+      ]
+
+      return strategyApplicationResult(
+        [...moveCommands, ...midInteractionCommands, ...onCompleteCommands],
+        {
+          grid: {
+            targetCell: targetGridCell,
+            draggingFromCell: draggingFromCell,
+            originalRootCell: originalRootCell,
+            currentRootCell: targetRootCell,
+          },
         },
-      })
+      )
+    },
+  }
+}
+
+function restoreGridTemplateFromProps(params: {
+  columns: GridAutoOrTemplateBase
+  rows: GridAutoOrTemplateBase
+}): PropertyToUpdate[] {
+  let properties: PropertyToUpdate[] = []
+  const newCols = printGridAutoOrTemplateBase(params.columns)
+  const newRows = printGridAutoOrTemplateBase(params.rows)
+  if (newCols === '') {
+    properties.push(propertyToDelete(PP.create('style', 'gridTemplateColumns')))
+  } else {
+    properties.push(propertyToSet(PP.create('style', 'gridTemplateColumns'), newCols))
+  }
+  if (newRows === '') {
+    properties.push(propertyToDelete(PP.create('style', 'gridTemplateRows')))
+  } else {
+    properties.push(propertyToSet(PP.create('style', 'gridTemplateRows'), newRows))
+  }
+  return properties
+}
+
+function getGridTemplates(jsxMetadata: ElementInstanceMetadataMap, gridPath: ElementPath) {
+  const grid = MetadataUtils.findElementByElementPath(jsxMetadata, gridPath)
+  if (grid == null) {
+    return null
+  }
+
+  const templateFromProps = grid.specialSizeMeasurements.containerGridPropertiesFromProps
+  const templateRowsFromProps = templateFromProps.gridTemplateRows
+  if (templateRowsFromProps == null) {
+    return null
+  }
+  const templateColsFromProps = templateFromProps.gridTemplateColumns
+  if (templateColsFromProps == null) {
+    return null
+  }
+
+  const templateCalculated = grid.specialSizeMeasurements.containerGridProperties
+  const templateRowsCalculated = templateCalculated.gridTemplateRows
+  if (templateRowsCalculated == null) {
+    return null
+  }
+  const templateColsCalculated = templateCalculated.gridTemplateColumns
+  if (templateColsCalculated == null) {
+    return null
+  }
+
+  return {
+    calculated: {
+      columns: templateColsCalculated,
+      rows: templateRowsCalculated,
+    },
+    fromProps: {
+      columns: templateColsFromProps,
+      rows: templateRowsFromProps,
     },
   }
 }