Add support for any type

[isra-fel]

Some services need to support any type, which means a property could be primitive types, object, array, etc.

autorest.powershell should support it to unblock some teams' migration.

[dolauli]

Swagger 2 does not support one-of/any. And the workaround is to define the property as an object without properties and additional properties in swagger.

[isra-fel]

These swagger extensions are a workaround to define any type in swagger v2 as if "one-of" in v3.

[isra-fel]

Tracked internally: Product Backlog Item 26117838: [PS] Autorest - support oneOf / anyOf