Add support for database functions introduced in 3.0 (#253)

* Add support for hash database functions

* Add support for Sign

django-stubs/db/models/functions/__init__.pyi

@@ -14,9 +14,14 @@ from .text import (
     Trim as Trim,
     Ord as Ord,
     Repeat as Repeat,
+    SHA1 as SHA1,
+    SHA224 as SHA224,
+    SHA256 as SHA256,
+    SHA384 as SHA384,
+    SHA512 as SHA512,
     StrIndex as StrIndex,
-    Replace as Replace,
     Substr as Substr,
+    Replace as Replace,
     Reverse as Reverse,
 )
 
@@ -81,6 +86,7 @@ from .math import (
     Power as Power,
     Radians as Radians,
     Round as Round,
+    Sign as Sign,
     Sin as Sin,
     Sqrt as Sqrt,
     Tan as Tan,

django-stubs/db/models/functions/math.pyi

@@ -23,3 +23,4 @@ class Round(Transform): ...
 class Sin(NumericOutputFieldMixin, Transform): ...
 class Sqrt(NumericOutputFieldMixin, Transform): ...
 class Tan(NumericOutputFieldMixin, Transform): ...
+class Sign(Transform): ...

django-stubs/db/models/functions/text.pyi

@@ -55,3 +55,11 @@ class Substr(Func):
 class Trim(Transform): ...
 class Upper(Transform): ...
 class Reverse(Transform): ...
+class MySQLSHA2Mixin: ...
+class OracleHashMixin: ...
+class PostgreSQLSHAMixin: ...
+class SHA1(OracleHashMixin, PostgreSQLSHAMixin, Transform): ...
+class SHA224(MySQLSHA2Mixin, PostgreSQLSHAMixin, Transform): ...
+class SHA256(MySQLSHA2Mixin, OracleHashMixin, PostgreSQLSHAMixin, Transform): ...
+class SHA384(MySQLSHA2Mixin, OracleHashMixin, PostgreSQLSHAMixin, Transform): ...
+class SHA512(MySQLSHA2Mixin, OracleHashMixin, PostgreSQLSHAMixin, Transform): ...