Cascade for restricted token view-table/view-database/view-instance operations (#2154)

Closes #2102

* Permission is now a dataclass, not a namedtuple - refs https://github.com/simonw/datasette/pull/2154/#discussion_r1308087800
* datasette.get_permission() method

datasette/permissions.py

@@ -1,6 +1,16 @@
-import collections
+from dataclasses import dataclass, fields
+from typing import Optional
 
-Permission = collections.namedtuple(
-    "Permission",
-    ("name", "abbr", "description", "takes_database", "takes_resource", "default"),
-)
+
+@dataclass
+class Permission:
+    name: str
+    abbr: Optional[str]
+    description: Optional[str]
+    takes_database: bool
+    takes_resource: bool
+    default: bool
+    # This is deliberately undocumented: it's considered an internal
+    # implementation detail for view-table/view-database and should
+    # not be used by plugins as it may change in the future.
+    implies_can_view: bool = False