Create string.pyi

Author: BobTheBuidler

mypyc/test-data/fixtures/string.pyi

@@ -0,0 +1,10 @@
+from typing import Optional
+
+class int: pass
+class str: pass
+    def count(
+        self,
+        substr: str,
+        start: Optional[int] = None,
+        end: Optional[int] = None,
+    ) -> int: pass