Allow file or directory picker APIs to be called without prior user gesture

For security reasons, the
showOpenFilePicker(),
showSaveFilePicker() and
showDirectoryPicker() web APIs
require a prior user gesture ("transient activation") to be called or will
otherwise fail.

With this policy set, admins can specify origins on which these APIs can be
called without prior user gesture.

For detailed information on valid url patterns, please see
https://chromeenterprise.google/policies/url-patterns/. * is
not an accepted value for this policy.

If this policy is unset, all origins will require a prior user gesture to call
these APIs.

Example value:

https://www.example.com
[*.]example.edu