Bug 1706561 Part 3: Make intern Handles hashable. r=gw
Bug 1706561 Part 3: Make intern Handles hashable. r=gw

This is needed to support the use of intern::Handle structs in hashable enums.

Differential Revision: https://phabricator.services.mozilla.com/D114556

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/62f10a2fceee997c573a197103d448227a614f05

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender