Fixes: gh-118
When the `BeanDefinition` for `Function` is a `FactoryBean`
(e.g. `GatewayProxyFactoryBean` in Spring Integration) and that
`BeanDefinition` isn't registered as `@Bean` method (e.g.
Spring Integration Java DSL parser), the `ContextFunctionCatalogAutoConfiguration`
doesn't resolve the target `Function` type properly
* Get the target `Function` bean type via `BeanFactory.getType(String)`
* Make fallback to the `Object.class` instead of bean type since we are
expecting here a generic type anyway
46fdca479b