Add a test to pin the 'enable default files' behavior of `dotnet run`

In https://github.com/dotnet/sdk/pull/50942 we removed `EnableDefaultItems=false` from the set of properties used to evaluate and run targets for Projects used as part of `dotnet run`. We did this to unblock Android use cases, where the Targets being run to compute the `run` command/arguments had a dependency on the default-includes behavior of the SDK. This is the _safest_ choice for us.

However, we need to capture that expectation in a unit test so we don't regress this behavior in the future. We should create a test that `dotnet run`'s a synthetic project with a `ComputeRunArguments` target that depends on a MSBuild Item that is included as part of the `EnableDefaultItems=true` setting. The Target could just fail if a given item wasn't found, for example.

Start at the dotnet run entry point and inspect how ComputeRunArguments evaluates targets for synthetic projects. Add a test project whose target depends on an item supplied by EnableDefaultItems=true; done means dotnet run succeeds and the target does not fail because that item is missing.

Written by the indexing model from the issue text.