import-checker: allow symbol imports from typing module
As we add typing annotations, we'll want to use a lot of symbols from
the `typing` module. Typing `typing` all the time will be annoying. Let's
allow symbol imports from this module.
While I was here, I changed some comments from "whitelist" to "allow list"
as the former is non-inclusive terminology.
Differential Revision: https://phab.mercurial-scm.org/D12365
{
// Enforcing
"eqeqeq" : true, // true: Require triple equals (===) for comparison
"forin" : true, // true: Require filtering for..in loops with obj.hasOwnProperty()
"freeze" : true, // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
"nonbsp" : true, // true: Prohibit "non-breaking whitespace" characters.
"undef" : true, // true: Require all non-global variables to be declared (prevents global leaks)
// Environments
"browser" : true // Web Browser (window, document, etc)
}