Add new --internal internal.db option, deprecate legacy _internal database

Refs:
- #2157 
---------

Co-authored-by: Simon Willison <swillison@gmail.com>

datasette/views/database.py

@@ -950,9 +950,9 @@ class TableCreateView(BaseView):
 
 
 async def _table_columns(datasette, database_name):
-    internal = datasette.get_database("_internal")
-    result = await internal.execute(
-        "select table_name, name from columns where database_name = ?",
+    internal_db = datasette.get_internal_database()
+    result = await internal_db.execute(
+        "select table_name, name from core_columns where database_name = ?",
         [database_name],
     )
     table_columns = {}

datasette/views/special.py

@@ -238,7 +238,7 @@ class CreateTokenView(BaseView):
         # Build list of databases and tables the user has permission to view
         database_with_tables = []
         for database in self.ds.databases.values():
-            if database.name in ("_internal", "_memory"):
+            if database.name == "_memory":
                 continue
             if not await self.ds.permission_allowed(
                 request.actor, "view-database", database.name