Breaking change in SelectMany props

Description

When addressing the issue in CMS-23405, a breaking change was introduced in how the values for string properties using SelectManyAttribute and ISelectionFactory are stored in the database. A change was made to serialize the selected options as JSON instead of comma separated strings. This change was reverted back to the original format. Make sure to verify that any values stored for properties using SelectManyAttribute are correct. Rechecking them in the UI and saving will save in the correct comma-separated format. Items saved in the JSON format introduced by 12.17.0 will not be selected correctly in the UI, so any updated properties needs to be verified.