Fix dashboard migration discrepancies between backend and frontend implementations (use toEqual) (#110268)

**Highlights**

* **Single-version migrations**: add `targetVersion` to migrator & model, separate outputs, enforce exact version.
* **Datasource fixes**: include `apiVersion` in tests, empty-string → `{}`, preserve `{}` refs, drop unwanted defaults.
* **Panel defaults & nesting**: only top-level panels get defaults; preserve empty `transformations` context-aware; filter repeated panels.

* **Migration parity**

  * V16: collapsed rows, grid height parsing (`px`).
  * V17: omit `maxPerRow` when `minSpan=1`.
  * V19–V20: cleanup defaults (`targetBlank`, style).
  * V23–V24: template vars + table panel consistency.
  * V28: full singlestat/stat parity, mappings & color.
  * V30–V36: threshold logic, empty refs, nested targets.
* **Save-model cleanup**: replicate frontend defaults/filtering, drop null IDs, metadata, unused props.
* **Testing**: unified suites, dev dashboards (v42), full unit coverage for major migrations.

Co-authored-by: Ivan Ortega [ivanortegaalba@gmail.com](mailto:ivanortegaalba@gmail.com)
Co-authored-by: Dominik Prokop [dominik.prokop@grafana.com](mailto:dominik.prokop@grafana.com)

apps/dashboard/pkg/migration/schemaversion/v16.go

@@ -97,12 +97,11 @@ func upgradeToGridLayout(dashboard map[string]interface{}) {
 		if showRows {
 			// add special row panel (lines 1041-1058 in TS)
 			rowPanel = map[string]interface{}{
-				"id":        nextRowID,
-				"type":      "row",
-				"title":     GetStringValue(row, "title"),
-				"collapsed": isCollapsed,
-				"repeat":    GetStringValue(row, "repeat"),
-				"panels":    []interface{}{},
+				"id":     nextRowID,
+				"type":   "row",
+				"title":  GetStringValue(row, "title"),
+				"repeat": GetStringValue(row, "repeat"),
+				"panels": []interface{}{},
 				"gridPos": map[string]interface{}{
 					"x": 0,
 					"y": yPos,
@@ -110,6 +109,12 @@ func upgradeToGridLayout(dashboard map[string]interface{}) {
 					"h": rowGridHeight,
 				},
 			}
+
+			// Set collapsed property only if the original row had a collapse property
+			// This matches the frontend behavior: rowPanel.collapsed = row.collapse
+			if _, hasCollapse := row["collapse"]; hasCollapse {
+				rowPanel["collapsed"] = isCollapsed
+			}
 			nextRowID++
 			yPos++
 		}