Cascade vendor prefix checks down to a property with no prefix.

[kelnos]

trafficstars

Right now we have most of our vendor extensions prefixed with the language or platform in use. So x-scala-type describes a custom type for Scala clients, and x-jvm-type does the same, but covers all JVM languages. We should also have x-type, which would apply to everything. (This is probably not useful for custom types, but would be useful for other properties, like the new x-{scala,java,jvm}-class-name extension.)

Referenced in a comment on https://github.com/twilio/guardrail/pull/719