The compiled functions implement that interface which means you can inspect
the signature of the method that created them and discover its
generic types.
These can be used to more reliably discover whether the user
has declared a function with flux types or "bare" POJOs. They
then pave the way to supporting single valued types in a special
way.
Also consolidate and simplify the logic in FunctionInspector
Should be easy enoug hto add back later, but it was causing issues
with type conversion where we are npot yet sophisticated enough
to chain functions together and keep track of the types being
passed between them.
Make it deployable via its maven coordinates in
spring-cloud-function-deployer (it is deployed by default on start
up right now, but that's just a demo)
* extracted FunctionGateway interface
* renamed current implementation to LocalFunctionGateway
* moved `compose` methods from FunctionGateway to FunctionRegistry
