Allow loading schema from SDL definition file as well as JSON

If passing a path to a file with a name that ends in ".graphql" or
".graphqls" (matching the filenames used in
[graphql-ruby](https://github.com/rmosolgo/graphql-ruby/blob/master/lib/graphql/schema.rb#L116)),
attempt to load the schema from that file assuming it's a schema
definition rather than a JSON schema.

Author: Tabby

lib/graphql/client.rb

@@ -54,6 +54,8 @@ def self.load_schema(schema)
       when String
         if schema.end_with?(".json") && File.exist?(schema)
           load_schema(File.read(schema))
+        elsif (schema.end_with?(".graphql", ".graphqls")) && File.exist?(schema)
+          GraphQL::Schema.from_definition(schema)
         elsif schema =~ /\A\s*{/
           load_schema(JSON.parse(schema, freeze: true))
         end

test/test_client_schema.rb

@@ -42,6 +42,12 @@ def test_load_schema_from_json_string
     assert_equal "AwesomeQuery", schema.query.graphql_name
   end
 
+  def test_load_schema_from_definition_string
+    definition = Schema.to_definition
+    schema = GraphQL::Client.load_schema(definition)
+    assert_equal "AwesomeQuery", schema.query.graphql_name
+  end
+
   def test_load_schema_ignores_missing_path
     refute GraphQL::Client.load_schema("#{__dir__}/missing-schema.json")
   end