We add an `onClick` function to allow the spoiler content to be revealed on click. This `onClick` function then removes the `spoiler` class and animates the "reveal" effect to display the text content. The spoiler tags will not be re-rendered until the messages are unmounted.
https://linear.app/comm/issue/ENG-2192/reveal-the-spoiler-content-on-click-within-a-message
Depends on D5599