Have @Form on method imply a bean is a "form bean" (not require @Form on method param)

[rbygrave]

Doing this because we can and this is likely that people do this a lot.
That is:

Treat FooForm method parameter as if was annotated with @Form (because it can't be anything else).

  @Post("other") @Form
  void postFormOther(FooForm fooForm, Context ctx) {
    ...
  }

---

The syntax implied by similarity to JAX-RS @BeanParam ... is to annotate the method parameter explicitly like below (which is what we support).

... but actually FooForm can't be anything but a "form bean" (it is not Java Context and not one of our known scalar types - String, Long, LocalDate ... etc).

  @Post("other") 
  void postFormOther(@Form FooForm fooForm, Context ctx) {
    ...
  }