fix(plugin-form-interaction-tracking-browser): Access element attributes through getAttribute

[Dogfalo]

Summary

Instead of accessing an element's attributes through it's object property, access it using getAttribute()
This is especially important in form elements where property values can be overridden by it's children inputs with that have an attribute name or id where the value matches property name.

Ex:

<form action="/form_submit.php">
  <input name="action" />
</form>

// console.log(form.action)
// <input name="action" />

Checklist

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