Getting Bluetooth to Work After Moving Boot Camp Partition to New Mac
Apparently the problem is that the "Apple Broadcom Built-in Bluetooth" driver is not the right one for the new hardware.  Here's what I did to fix it:


Open Device Manager, open the Bluetooth Radios subtree, right-click the "Apple Broadcom Built-in Bluetooth" icon, and choose the "Update Driver Software..." menu item.
Choose "Browse my computer for driver software"
Choose "Let me pick from a list of device drivers on my computer"
Select "Apple Inc." for Manufacturer, and "Apple Built-in Bluetooth" for Model, and click Next.


After the driver installed, "Apple Broadcom Built-in Bluetooth" had been replaced by "Apple Built-in Bluetooth" and "Microsoft Bluetooth Enumerator" in the Bluetooth Radios subtree of Device Manager, and I was then able to use the Add a device wizard to set up my Bluetooth mouse and keyboard.