Top-level statements

Allow a sequence of statements to occur right before the namespace_member_declarations of a compilation_unit (i.e. source file).

The semantics are that if such a sequence of statements is present, the following type declaration, modulo the actual type name and the method name, would be emitted:

static class Program
{
    static async Task Main()
    {
        // statements
    }
}

Proposal: https://github.com/dotnet/csharplang/blob/main/proposals/top-level-statements.md Open issues and TODOs are tracked at https://github.com/dotnet/roslyn/issues/41704. Test plan: https://github.com/dotnet/roslyn/issues/43563. See also https://github.com/dotnet/csharplang/issues/3117.