Allow screen capture without prior user gesture

For security reasons, the
getDisplayMedia() web API requires
a prior user gesture ("transient activation") to be called or will otherwise
fail.

With this policy set, admins can specify origins on which this API 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
this API.

Example value:

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