Support Int128 and UInt128 in schema generation

[captainsafia]

.NET 7 adds support for representing 128-bit integers via the Int128 and UInt128 types.

When provided as inputs for an API, the schema generator interprets the type as a string. When emitted as part of the response, the type is treated as an object.

We probably want to represent this type using the { "type": "integer" } schema type.

See dotnet/aspnetcore#43119 for more info.