keep @oneOf and input value @deprecated in IntrospectionResultToSchema - #4514

Spock, a schema with input UserLookup @oneOf { byId: ID byEmail: String } run through IntrospectionQuery.INTROSPECTION_QUERY, IntrospectionResultToSchema.createSchemaDefinition, AstPrinter and SchemaGenerator:

(rebuilt.getGraphQLSchema().getType("UserLookup") as GraphQLInputObjectType).isOneOf()
 |       |                  |                                                |
 |       |                  GraphQLInputObjectType{name='UserLookup', ...}   false

createInputObject never reads __Type.isOneOf, so the rebuilt schema has a plain input object and { user(lookup: {byId: "1", byEmail: "a@b.c"}) } passes validation and reaches the data fetcher, where the origin schema rejects it with Exactly one key must be specified for OneOf type 'UserLookup'. the default introspection query asks for isOneOf, and also for isDeprecated / deprecationReason on arguments and input fields, which createInputValueDefinitions drops the same way while fields, enum values and directive definitions keep theirs. graphql-js buildClientSchema carries isOneOf and input value deprecation over.

createInputObject now adds @oneOf when isOneOf is true and input values go through the existing createDeprecatedDirective. the regression tests in IntrospectionResultToSchemaTest fail before the change.