MBS Xojo Plugins, version 21.4pr4

New in this prerelease of the 21.4 plugins:

Add thread pooling for Windows to be used for multi threaded methods.
Added SharingPanelMBS class for sharing on iOS.
Fixed a crash in JSONMBS class returning big JSON arrays.
Fixed problem on Windows with GraphicsMagick initialization.
Updated DynaPDF to version 4.0.58.153.
Moved WindowsQOSMBS class into its own plugin part, split from WindowsProxy plugin part.
Implemented thread pool for Windows to be used for our MT methods, so threads get reused.