Python: Allow list_splats as type annotations

That is, the `*T` in `def foo(*args : *T): ...`.

This is apparently a piece of syntax we did not support correctly until
now.

In terms of the grammar, we simply add `list_splat` as a possible
alternative for `type` (which could previously only be an `expression`).
We also update `python.tsg` to not specify `expression` those places (as
the relevant stanzas will then not work for `list_splat`s).

This syntax is not supported by the old parser, hence we only add a new
parser test for it.

python/extractor/tests/parser/functions_new.expected

@@ -0,0 +1,41 @@
+Module: [1, 0] - [3, 0]
+  body: [
+    Assign: [1, 0] - [1, 42]
+      targets: [
+        Name: [1, 4] - [1, 26]
+          variable: Variable('tuple_typed_list_splat', None)
+          ctx: Store
+      ]
+      value:
+        FunctionExpr: [1, 0] - [1, 42]
+          name: 'tuple_typed_list_splat'
+          args:
+            arguments
+              defaults: []
+              kw_defaults: []
+              annotations: []
+              varargannotation:
+                Starred: [1, 35] - [1, 40]
+                  value:
+                    Name: [1, 36] - [1, 40]
+                      variable: Variable('ARGS', None)
+                      ctx: Load
+                  ctx: Load
+              kwargannotation: None
+              kw_annotations: []
+          returns: None
+          inner_scope:
+            Function: [1, 0] - [1, 42]
+              name: 'tuple_typed_list_splat'
+              type_parameters: []
+              args: []
+              vararg:
+                Name: [1, 28] - [1, 32]
+                  variable: Variable('args', None)
+                  ctx: Param
+              kwonlyargs: []
+              kwarg: None
+              body: [
+                Pass: [2, 4] - [2, 8]
+              ]
+  ]

python/extractor/tests/parser/functions_new.py

@@ -0,0 +1,2 @@
+def tuple_typed_list_splat(*args : *ARGS):
+    pass