Handles the debugModeInspectableWebView extra property for webviewController: parses the raw
value, validates it, checks platform support, and applies it (enabling Safari Web Inspector
debugging on iOS, requires iOS 16.4+; no-op on Android). Shared by the Classic and Web
integrations so the parse/guard/log logic exists once.
Set the extra properties for a unit
Stores locally with unit-level tag (always overwrites page/global)
Returns a set of property keys that were updated