Add triple-slash types reference to trusted-types.

[reduckted]

Summary

Fixes #1035.

We need to tell TypeScript that we use the type declarations from trusted-types. This is done using a triple-slash directive. Without this, the references to trusted-types in the type declaration file can cause compilation errors for certain configurations.

I initially added /// <reference types="trusted-types" preserve="true"/> to the top of purify.ts. Doing that resulted in the triple-slash directive being included in the type declaration files as expected, but it also ended up in the compiled JavaScript, but not at the top of the file (I think due to Rollup combining files together). To keep those files clean I've opted to add this directive via the fix-types.js script (previously called fix-cjs-types.js).

I've also installed @types/node as a dev dependency so that fix-types.js can have type checking performed to help avoid any mistakes when editing that file.

[cure53]

Thanks a ton, again! 🙇