Add trusted-types and require-trusted-types-for CSP Directive

[KyFaSt]

All PRs:

• [x] Has tests
• [ ] Documentation updated

Adding a new CSP directive

This PR adds support for the TrustedTypes CSP directives, require-trusted-types-for and 'trusted-types'.

• Is the directive supported by any user agent? If so, which? TrustedTypes are available in Chrome 83, Edge 83 and a polyfill exists for browsers that don't currently support.

• What does it do? require-trusted-types-for disallows using strings with DOM XSS injection sink functions (functions like Document.write, Element.InnerHtml), and requires matching types created by Trusted Type policies.

• What are the valid values for the directive require-trusted-types-for only allows script. trusted-types allows a list of strings, including one 'allow-duplicates' which allows multiples of the same named policy to be created.