tsec is a TypeScript compiler wrapper for restricting use of
security-sensitive DOM APIs, in particular those that could lead to XSS
or Trusted Types violations. Add it as a linter to aio to prevent future
Trusted Types regressions on angular.io.
Also introduces security_exemptions.json, which lists the known,
security-reviewed tsec security violations. New entries can only be
added to this file after a security review, in particular making sure
that the corresponding code does not cause XSS vulnerabilities or
Trusted Types violations.
PR Close#42800
