Design enhancement: a catch-all class decorator for modifications to modelSchema (which would subsume e.g. `serializeAll`)

[peey]

serializeAll is not the only case which is insufficiently supported by class field decorators.

factory is another case. Without decorator support, this is what the user has to write:

getDefaultModelSchema(Todo).factory = context => (...)

but with decorator support, this is what user may instead write

@factory(context => (...))
class Todo {
  ...
}

But this got me thinking, shouldn't there be just one class-decorator to support both of these?

@serializr(() => {factory: ..., {props: {"*": true}}) 

The returned value could just be deep-merged into the model-schema as built-up by field decorators.

It does not save many characters of typing, but it's a much more uniform interface for the library user. Of the two interfaces offered by the library (decorator-based and non-decorator), it'll be ideal if the user using one of the interfaces doesn't have to deal with the other.