Tools/mypy: Enforce typed generics in tools/run-mypy.

This adds the "--disallow-any=generics" option to run-mypy, which no
longer permits:
- inheriting from "list"; use "List[sometype]" (or a TypeVar)
- generic types with no following square brackets specifying the type
  (even if initially 'Any')

Any (and '...' for Callable) is a lot easier to search for than an
absence of square brackets, and should improve overall typing quality.

tools/run-mypy

@@ -87,7 +87,8 @@ if not python_files:
 extra_args = ["--check-untyped-defs",
               "--follow-imports=silent",
               "--scripts-are-modules",
-              "-i", "--cache-dir=var/mypy-cache"]
+              "-i", "--cache-dir=var/mypy-cache",
+              "--disallow-any=generics"]
 if args.linecoverage_report:
     extra_args.append("--linecoverage-report")
     extra_args.append("var/linecoverage-report")