* test: add DataFormat.CreateInProcessFormat tests
Cover the new InProcess format API: kind, identifier, null/empty
validation, non-ASCII identifiers, HasSystemName for all four kinds,
ToSystemName throwing, equality/inequality, DataTransferItem
integration, and coexistence with other formats in DataTransfer.
* feat: implement DataFormat.CreateInProcessFormat<T> for in-process drag/drop
Add DataFormatKind.InProcess and DataFormat.CreateInProcessFormat<T>()
so users can pass arbitrary object references during in-process
drag-and-drop without crossing serialization boundaries.
- Add HasSystemName property to indicate whether ToSystemName() is valid
- Update ToSystemName to throw for InProcess (same as Universal)
- Guard all 7 platform backends (Win32, macOS, X11, Android, Browser,
iOS) to skip InProcess formats during clipboard/drag-drop enumeration
Closes#20097
* fix: remove HasSystemName API per review feedback
Nathan Nguyen