[filters] `toArray` and `getFields` should account for composite array of filters

[rauanmayemir]

Currently, calling both getFields and toArray returns child fields as is, leaving you with an array of unwrapped filter objects.

I think filters should somehow check the schema and serialize nested objects.

[vvval]

@rauanmayemir are you sure? according to toArray() functionality, its output is a plain data array, all objects are converted to values

[rauanmayemir]

@vvval Not if you have a field that is an array of filter objects.