This change allows the RBTools for Windows installer to build on modern

Windows systems, with the latest versions of the .NET Framework SDK,

the Windows SDK, and Visual Studio Build Tools.
This is tested on a Windows Server 2022 build VM.
Common WiX property groups have been moved out into common.props, to

help with maintenance. These property groups define some common

directories, file paths, and signing information used by both

bootstrapper.wixproj and rbtools.wixproj.
The modern MSBuild.exe from Visual Studio Build Tools is now used,

instead of the older version from the .NET Framework SDK. The latter

doesn't work with modern versions of the Windows SDK, and crashes. We

discover this in build-installer.bat by using Visual Studio's

vswhere utility, as documented by Microsoft. This should be more

future-proof.
It also drops support for the 32-bit installer. As nearly all systems

are going to be 64-bit these days, and given our target version of

Python 3.10 (which will be in another change), it doesn't seem to make

much sense to continue shipping 32-bit support.

Successfully built the RBTools for Windows installer on Windows Server

2022 with the latest versions of all SDKs and tools.