[Clean-up] Remove all extraneous warnings

[michael-hawker]

We have a lot of warnings MSB4011 in the project about duplicated includes for props files.

There's also an MSB3277 about different versions of System.Collections.Immutable.

These extra warnings make it more difficult to see analyzer warnings and other style issues which may get flagged by the IDE. We should aim for having no extraneous warnings in the project so we know when we have a clean build.

[mrlacey]

The MSB4011 warnings will need to be suppressed as the projects in the solution need to explicitly include some things that should get included automatically but aren't always.

[michael-hawker]

@mrlacey did you want to add the suppression then and then investigate any of the remaining warnings?

[mrlacey]

As per the details at dotnet/msbuild#4038 MSB4011 cannot be suppressed by properties, only from the command line.
It can be suppressed in the CI server scripts but VS is always going to report these. Not sure if it's worth documenting anywhere.

[michael-hawker]

Nice find @mrlacey, thanks. Not sure we can work around them as we use the props for dependency management as well, so they're going to get included multiple times. I've added a comment to the linked issue.

[mrlacey]

Removing my assignment as future work on this is unscheduled and to allow for someone else to look at it if they wish.

[michael-hawker]

Thanks @mrlacey. I know @azchohfi was curious if we could make improvements to the props file structure here to cause these errors not to occur as well. We can pick this up later since it's all internalized from the templates (I think).

I think we could investigate in the future using a custom property defined in MSBuild, then only import certain files if that's not defined. I think I've seen that in the SDK props files to make sure a particular props is only defined once as the property gets set by the props file, and then other imports ignore it later in the pipeline.

[mrlacey]

Some of the dependency issues are due to the use of Directory.Build.props files that are included automatically but also included explicitly by some of the other props files.
Now I'm wondering if it's possible to just use props files that are included explicitly to avoid this issue. @Arlodotexe did you look at this when setting up the props files?