gh-111545: Test PyHash_GetFuncDef() function (#112098)

Add Modules/_testcapi/hash.c and Lib/test/test_capi/test_hash.py.

Doc/c-api/hash.rst

@@ -0,0 +1,48 @@
+.. highlight:: c
+
+PyHash API
+----------
+
+See also the :c:member:`PyTypeObject.tp_hash` member.
+
+.. c:type:: Py_hash_t
+
+   Hash value type: signed integer.
+
+   .. versionadded:: 3.2
+
+.. c:type:: Py_uhash_t
+
+   Hash value type: unsigned integer.
+
+   .. versionadded:: 3.2
+
+
+.. c:type:: PyHash_FuncDef
+
+   Hash function definition used by :c:func:`PyHash_GetFuncDef`.
+
+   .. c::member:: Py_hash_t (*const hash)(const void *, Py_ssize_t)
+
+      Hash function.
+
+   .. c:member:: const char *name
+
+      Hash function name (UTF-8 encoded string).
+
+   .. c:member:: const int hash_bits
+
+      Internal size of the hash value in bits.
+
+   .. c:member:: const int seed_bits
+
+      Size of seed input in bits.
+
+   .. versionadded:: 3.4
+
+
+.. c:function:: PyHash_FuncDef* PyHash_GetFuncDef(void)
+
+   Get the hash function definition.
+
+   .. versionadded:: 3.4

Doc/c-api/utilities.rst

@@ -17,6 +17,7 @@ and parsing function arguments and constructing Python values from C values.
    marshal.rst
    arg.rst
    conversion.rst
+   hash.rst
    reflection.rst
    codec.rst
    perfmaps.rst