Deprecate pallets stubs (#5424)

Part of #5423

* Support new metadata fields in check_consistent

stubs/Flask/METADATA.toml

@@ -1,3 +1,4 @@
 version = "0.1"
 python2 = true
 requires = ["types-Jinja2", "types-Werkzeug", "types-click"]
+obsolete_since = "2.0"

stubs/Jinja2/METADATA.toml

@@ -1,3 +1,4 @@
 version = "0.1"
 python2 = true
 requires = ["types-MarkupSafe"]
+obsolete_since = "3.0"

stubs/MarkupSafe/METADATA.toml

@@ -1,2 +1,3 @@
 version = "0.1"
 python2 = true
+obsolete_since = "2.0"

stubs/Werkzeug/METADATA.toml

@@ -1,3 +1,4 @@
 version = "0.1"
 python2 = true
 requires = []
+obsolete_since = "2.0"

stubs/click/METADATA.toml

@@ -1,2 +1,3 @@
 version = "0.1"
 python2 = true
+obsolete_since = "8.0"

stubs/itsdangerous/METADATA.toml

@@ -1,2 +1,3 @@
 version = "0.1"
 python2 = true
+obsolete_since = "2.0"

tests/check_consistent.py

@@ -21,6 +21,7 @@ consistent_files = [
     {"stdlib/@python2/builtins.pyi", "stdlib/@python2/__builtin__.pyi"},
     {"stdlib/threading.pyi", "stdlib/_dummy_threading.pyi"},
 ]
+metadata_keys = {"version", "python2", "python3", "requires", "extra_description", "obsolete_since"}
 
 
 def assert_stubs_only(directory):
@@ -161,9 +162,7 @@ def check_metadata():
         major, minor = version.split(".")
         assert major.isdigit() and minor.isdigit(), msg
         for key in data:
-            assert key in {
-                "version", "python2", "python3", "requires"
-            }, f"Unexpected key {key} for {distribution}"
+            assert key in metadata_keys, f"Unexpected key {key} for {distribution}"
         assert isinstance(data.get("python2", False), bool), f"Invalid python2 value for {distribution}"
         assert isinstance(data.get("python3", True), bool), f"Invalid python3 value for {distribution}"
         assert isinstance(data.get("requires", []), list), f"Invalid requires value for {distribution}"