Move assembly attributes to props file

[Arlodotexe]

Background

To facilitate testing, we define the [InternalsVisibleTo] attribute on the assembly of each project.

Problem

We're currently use C# to do this, which puts another file into the solution explorer for every experiment.

Solution

We can define InternalsVisibleTo via MSBuild props file. We should do this to clean up the solution explorer for the user.

Relevant documentation:
https://learn.microsoft.com/en-us/dotnet/core/project-sdk/msbuild-props#internalsvisibleto

[michael-hawker]

From CommunityToolkit/Labs-Windows#326 and the PR to fix it in CommunityToolkit/Labs-Windows#327 we figured out how to generate AssemblyMetadata attributes as part of the MSBuild project to not have to have so many AssemblyInfo.cs files in our projects.

We can use this approach for InternalVisibleTo as well and remove the AdditionalAssemblyInfo.cs files in the library projects.

Related to #15

[michael-hawker]

@niels9001 discovered that when we changed parts of the templates namespaces/assemblies for the tests that we missed updating the internalsvisibleto attributes.

We should fix this as we're moving these files to the props.

We need to remove Experiment from the template here (not sure if we use that anywhere for lookup - think that's just the samples):

Tooling-Windows-Submodule/ProjectTemplate/tests/ExampleProjectTemplateTestClass.cs

Line 9 in 365f01d

namespace ProjectTemplateExperiment.Tests;

And ensure the internals are visible to these assemblies:

Tooling-Windows-Submodule/ProjectHeads/SingleComponent/Tests.Uwp/ProjectTemplate.Tests.Uwp.csproj

Line 30 in 365f01d

<AssemblyName>ProjectTemplateExperiment.Tests.Uwp</AssemblyName>

Tooling-Windows-Submodule/ProjectHeads/SingleComponent/Tests.WinAppSdk/ProjectTemplate.Tests.WinAppSdk.csproj

Line 28 in 365f01d

<AssemblyName>ProjectTemplateExperiment.Tests.WinAppSdk</AssemblyName>

Tooling-Windows-Submodule/ProjectHeads/AllComponents/Tests.Uwp/CommunityToolkit.Tests.Uwp.csproj

Line 31 in 365f01d

<AssemblyName>CommunityToolkit.Tests.Uwp</AssemblyName>

Tooling-Windows-Submodule/ProjectHeads/AllComponents/Tests.WinAppSdk/CommunityToolkit.Tests.WinAppSdk.csproj

Line 28 in 365f01d

<AssemblyName>CommunityToolkit.Tests.WinAppSdk</AssemblyName>