Introduce msbuild/toolset selection log switch for arcade

[mmitche]

• This issue is blocking
• This issue is causing unreasonable pain

Every once in a while, we need to figure out why arcade is choosing a specific dotnet, arcade, msbuild, etc. The logic for the selection has grown organically over the years to support many different scenarios, and debugging why a specific engine was chosen can be pretty hard.

Introduce a switch or env-var to log the process. This will save a lot of time over the long haul.

[missymessa]

@mmitche do you think this work can be done as part of the VMR effort?

[mmitche]

Yes, let me assign to that board.