Cython binding for FBString

Summary: only exporting `toStdString` API for now, which is most useful in exposing FBString to Python land

Reviewed By: Filip-F

Differential Revision: D34402501

fbshipit-source-id: 6ebe53b346e6be037493abb712edbc301ea06ef6

folly/python/fbstring.pxd

@@ -0,0 +1,21 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from libcpp.string cimport string
+
+cdef extern from "folly/FBString.h" namespace "folly":
+    cdef cppclass basic_fbstring[T]:
+        string toStdString()
+
+ctypedef basic_fbstring[char] fbstring