Provide analyzer for removing unneeded public partial class Program

[captainsafia]

Follow-up to https://github.com/dotnet/aspnetcore/pull/58199.

Based on the code generation that we introduced earlier, users can get rid of the explicit public partial class Program { } declarations in their source code and rely on the new default behavior.

This PR introduces an analyzer to find these explicit declarations and a code fixer to remove them.

Implements https://github.com/dotnet/aspnetcore/issues/58488