With the implementation of Spoilers on both `web` and `native`, we want to prevent the spoiler text from being revealed in `MessagePreview` on both platforms. This diff handles replacing the text enclosed with spoiler characters with three black squares, as discussed in the parent tasks for Spoilers, [ENG-1472](https://linear.app/comm/issue/ENG-1472/spoiler-quotes-in-markdown). We previously thought about replacing the spoilers with black square emojis.
The idea with this diff is to "intercept" the raw message text before it is parsed for markdown rules, so we can replace the text enclosed within `|| ... ||` before the spoiler characters are removed for the message preview.
[Context Diff](https://phab.comm.dev/D693)
Addresses [ENG-2193](https://linear.app/comm/issue/ENG-2193/prevent-spoiler-text-from-appearing-in-messagepreview-[web])
Addresses [ENG-2055](https://linear.app/comm/issue/ENG-2055/prevent-spoiler-text-from-appearing-in-messagepreview-[native])
The reason for not using `spoilerRegex` is that `/^\|\|([^\n]+?)\|\|/g` parses for the spoilers located at the start of the string since there is an [anchor](https://www.regular-expressions.info/anchors.html), but instead we're trying to just find all instances of spoiler text in a string and replace that, so we use different RegEx.