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/v21.go

@@ -3,8 +3,6 @@ package schemaversion
 import (
 	"context"
 	"strings"
-
-	"github.com/grafana/grafana/apps/dashboard/pkg/migration/utils"
 )
 
 // V21 migrates data links to replace __series.labels with __field.labels.
@@ -82,7 +80,7 @@ func V21(_ context.Context, dashboard map[string]interface{}) error {
 
 func updateDataLinks(options map[string]interface{}) {
 	dataLinks, ok := options["dataLinks"].([]interface{})
-	if !ok || !utils.IsArray(dataLinks) {
+	if !ok || !IsArray(dataLinks) {
 		return
 	}