Folders: Use folder UID when deleting library elements in folder (#98967)

* Refactor  deleteLibraryElementsInFolderUID to use folder UID only
* Convert dashboard error to folder one when deleting library elements
* Fix incorrectly set folder UID in nested folder test

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Co-authored-by: kay delaney <45561153+kaydelaney@users.noreply.github.com>

pkg/services/folder/folderimpl/folder_test.go

@@ -734,7 +734,7 @@ func TestIntegrationNestedFolderService(t *testing.T) {
 					_ = createRule(t, alertStore, subfolder.UID, "sub alert")
 					// nolint:staticcheck
 					libraryElementCmd.FolderID = subfolder.ID
-					libraryElementCmd.FolderUID = &subPanel.FolderUID
+					libraryElementCmd.FolderUID = &subfolder.UID
 					subPanel, err = lps.LibraryElementService.CreateElement(context.Background(), &signedInUser, libraryElementCmd)
 					require.NoError(t, err)
 				}