Flattening out inputs about rejoiner HOT 1 OPEN

I like the idea of providing a setting to flatten out inputs, I'm not sure where the best place to add that option is. The actual change should be pretty simple.

Input schema modifications is a requirement that came up for us too. ProtoRegistry.modifyTypes() could be modified to apply modifications to input types. Either TypeModification can be modified to support input types or a new InputTypeModification could be added. I'm thinking InputTypeModification would be better. Since a proto can be used as both output and input GraphQL types this would allow TypeModifications to only modify the output types and InputTypeModifications to only modify input types.

from rejoiner.