Angular-internal type definitions for Trusted Types were added in #39211.
When compiled using the Closure compiler with certain optimization
flags, identifiers from these type definitions (such as createPolicy)
are currently uglified and renamed to shorter strings. This causes
Angular applications compiled in this way to fail to create a Trusted
Types policy, and fall bock to using strings.
To fix this, mark the internal Trusted Types definitions as declarations
using the "declare" keyword. Also convert types to interfaces, for
the reasons explained in https://ncjamieson.com/prefer-interfaces/
PR Close#39471
f54662e931