Port SDL validation benchmark

From src/validation/__tests__/validateSDL-benchmark.js

Author: ktosiek

tests/benchmarks/test_validate_sdl.py

@@ -0,0 +1,11 @@
+from graphql import parse
+from graphql.validation.validate import validate_sdl
+
+# noinspection PyUnresolvedReferences
+from ..fixtures import big_schema_sdl  # noqa: F401
+
+
+def test_validate_sdl_document(benchmark, big_schema_sdl):  # noqa: F811
+    sdl_ast = parse(big_schema_sdl)
+    result = benchmark(lambda: validate_sdl(sdl_ast))
+    assert result == []