Add a module that provides a Trusted Types policy for use internally by
Angular. The policy is created lazily and stored in a module-local
variable. For now the module does not allow configuring custom policies
or policy names, and instead creates its own policy with 'angular' as a
fixed policy name. This is to more easily support tree-shakability.
Helper functions for unsafely converting strings to each of the three
Trusted Types are also introduced, with documentation that make it clear
that their use requires a security review. When Trusted Types are not
available, these helper functions fall back to returning strings.
PR Close#39207
0875fd2360