Nullness - Consider supporting Nullable shorthand for TreatWarningsAsErrors

**Is your feature request related to a problem? Please describe.**

In C# it's possible to convert all nullable-related warnings to errors using `nullable`. From [docs](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/compiler-options/errors-warnings#treatwarningsaserrors):
`
The set of all nullability warnings can be specified with the Nullable shorthand.
`

So in line with https://github.com/dotnet/fsharp/pull/17486 it would be nice to have WAE behaviour as well.

**Describe the solution you'd like**

Support `nullable`

**Describe alternatives you've considered**

Just use specific warning numbers or even `true`.

**Additional context**

.