namespace_or_type_name is not permitted to reference a static class in a using_directive

**Describe the bug**

[C# 7 subclause 7.8.1](https://github.com/dotnet/csharpstandard/blob/standard-v7/standard/basic-concepts.md#781-general) does not permit a *namespace_or_type_name* to reference a static class when it is in a *using_alias_directive* ([14.5.2](https://github.com/dotnet/csharpstandard/blob/standard-v7/standard/namespaces.md#1452-using-alias-directives)) or a *using_static_directive* ([14.5.4](https://github.com/dotnet/csharpstandard/blob/standard-v7/standard/namespaces.md#1454-using-static-directives)). Those uses are not part of [this list in 7.8.1](https://github.com/dotnet/csharpstandard/blob/02d1a90122ece425cff575f47f197fb396be73d4/standard/basic-concepts.md?plain=1#L896-L899):

> A *namespace_or_type_name* is permitted to reference a static class ([§15.2.2.4](https://github.com/dotnet/csharpstandard/blob/standard-v7/standard/classes.md#15224-static-classes)) only if
>
> * The *namespace_or_type_name* is the `T` in a *namespace_or_type_name* of the form `T.I`, or
> * The *namespace_or_type_name* is the `T` in a *typeof_expression* ([§12.8.17](https://github.com/dotnet/csharpstandard/blob/standard-v7/standard/expressions.md#12817-the-typeof-operator)) of the form `typeof(T)`

**Example**

This is allowed by 14.5.2 and 14.5.4 but not by 7.8.1.

```csharp
using A = N.S;
using static N.S;

namespace N
{
static class S
{
}
}
```

**Expected behavior**

7.8.1 should allow a *namespace_or_type_name* to reference a static class in these additional cases:

* The *namespace_or_type_name* is in a *using_alias_directive* (14.5.2).
* The *namespace_or_type_name* is the *type_name* in a *using_static_directive* (14.5.4).

**Additional context**

14.5.2 references *namespace_or_type_name* in the definition of *using_alias_directive*:

14.5.4 references *type_name* in the definition of *using_static_directive*:

7.8.1 explains that a *type_name* is a *namespace_or_type_name*:

Inspired by .