Update GraphQL mutation compiler to consider arguments with replace_null_with_default

[dom-binti]

Motivation

With graphql-ruby arguments, you can set required: false, default_value: 'foo', replace_null_with_default: true to fill a null sent by a client with the default value (docs). The current graphql mutation compiler doesn't take this into account, and assumes that all required: false arguments are nilable, when in reality a non-nil default_value plus replace_null_with_default means the resolver will always receive a non-nil value.

Implementation

I updated GraphqlTypeHelper.type_for to take in a GraphQL::Schema::Argument, rather than just the argument type, and check for the other Argument params when deciding if the type is nilable.

Tests

Added a test with both a nil and a non-nil default_value to the existing graphql mutation compiler tests.

[dom-binti]

I have signed the CLA!

[KaanOzkan]

LGTM but I'd like to test it with our monolith quickly before shipping when the CI passes.

[dom-binti]

@KaanOzkan sgtm. Looks like CI is passing now. Let me know if there's anything else to do on my end!

[KaanOzkan]

Looks like our monolith doesn't utilize replace_null_with_default. Existing RBIs are unchanged. Thanks for the contribution.