Upgrade IIS C++ projects to build with platformtoolset v142 (VS2019)

[natemcmaster]

Depends on #7005

Let's update the C++ projects for ANCM to build with the Visual Studio 2019 toolset. This should be a matter of updating the .vcxproj and reacting to any warnings or errors the new toolset finds.

<PlatformToolset>v142</PlatformToolset>

[analogrelay]

Looks like there are a few still using v141 (https://github.com/aspnet/AspNetCore/search?q=PlatformToolset%3Ev141&unscoped_q=PlatformToolset%3Ev141). @jkotalik do you know off-hand if there's a reason for this?

Everything else appears to be on v142

[jkotalik]

They are part of IIS Setup (a repo we source copied). I think I can update them without any problem.

[analogrelay]

Certainly worth a try. I'll put it in preview 6 since it shouldn't impact customer experience.

[analogrelay]

Re-opening this. We still have some projects using 141. I do think we can punt this out a bit though since I don't know that there's a pressing reason to update.