Add `prevent-textContent` scriptlet

@description
 Conditionally prevent assignment to `textContent` property.

 @param [selector]
 Optional. The element must matches `selector` for the prevention to take
 place.

 @param [pattern]
 Optional. A pattern to match against the assigned value. The pattern can be
 a plain string, or a regex. Prepend with `!` to reverse the match condition.