Investigate Wix5's compatibility with existing SignTool methodology

[mmitche]

Today, when an installer is built, we capture the set of input files and command line (.dlls, wixobj, etc.) sent to the linker command (light.exe) in a zip file (.wixpack.zip). SignTool sees an .msi, finds the corresponding wixpack.zip, signs the contents of the wixpack (.dlls), and then calls the original light.exe command using the modified input. This works flawlessly today. This may not work with Wix5 due to how the toolset is constructed.

This issue covers investigation of how Wix5 might fit into the existing model.