Add support for MSVC "Visual Studio 2022 Preview channel"

Microsoft regularly publishes beta "preview" versions of MSVC, expanding the features covered in C and C++ languages, and sometimes changing the behavior of the command-line tool `cl.exe`. I'm using this preview release to test for bugs and missing features of the compiler, in order not have to report already fixed bugs, and be up-to-date w.r.t. new behaviors of the compiler. It would be quite useful to have access to the preview channel of MSVC in godbolt.org!
I don't know how the infrastructure's set up, but a first step could be to switch the install channel to `Visual Studio 2022 Preview channel` using Visual Studio Installer [`--channelUri` or `--channelId`](https://learn.microsoft.com/en-us/visualstudio/install/command-line-parameter-examples?view=vs-2022#using---channeluri) to (respectively) `https://aka.ms/vs/17/pre/channel` and `VisualStudio.17.Preview`.
This would also bring the support on par with other compilers, for which the `trunk` branch is already available in godbolt.
Thanks for the hard work!

No repository file, test, or entry point is named. Start by locating the Visual Studio Installer configuration for MSVC, then verify how the channel is selected and how compiler availability is checked; done means the Visual Studio 2022 Preview channel is available in Compiler Explorer alongside existing MSVC versions.

Written by the indexing model from the issue text.