Improve trusted-replace-xhr-response and prevent-xhr — randomise thisArg.shouldBePrevented

[AdamWr]

Currently it's too easy to disable trusted-replace-xhr-response and prevent-xhr by adding <xhr>.shouldBePrevented = false;

Steps to reproduce:

1. Add this rule:

   example.org#%#//scriptlet('trusted-replace-xhr-response', '*', 'TEST', '/')

2. Go to - https://example.org/
3. In browser console run:

   (() => {
   function reqListener() {
   alert(this.responseText);
   }
   const xhr = new XMLHttpRequest();
   xhr.addEventListener("load", reqListener);
   xhr.open("GET", "/");
   xhr.shouldBePrevented = false;
   xhr.send();
   })();

If scriptlet works correctly there should be an alert with TEST message, but xhr.shouldBePrevented = false; disables scriptlet and content is not replaced.

I guess that adding random part to: https://github.com/AdguardTeam/Scriptlets/blob/bad388d94ab265ffd61d23b26a8637721fabfc1e/src/scriptlets/trusted-replace-xhr-response.js#L123 something like thisArg.shouldBePrevented_<random> should fixes it.