feat: add Matrix -> Discord reactions

[mangofeet]

Implements reactions from matrix to discord, intended for cases where a single matrix user is using the bot as a personal puppet

Functionality is disabled by default and enable by setting bridge.enableMatrixReactions to true

• Send reactions to discord from Matrix to Discord
• Removes reactions when redacted in Matrix
• Handle thumbs up exception from Matrix to Discord
• Handle thumbs up exception from Discord to Matrix

[jaller94]

Looking forward to Discord reactions. 👏
Do you have everything you need to finish the PR?

[jaller94]

Nice optimisation for having to build the first step less often. 👍

[mangofeet]

Wasn't sure if this should go in it's own PR, I was going to revert it, but yeah, it does speed up building by quite a bit when trying to test changes on a remote machine instead of locally.

EDIT: There's a way to make it even faster by adding just the package.json and yarn.lock files, doing the yarn install, then adding the source code and doing the build separately

[mangofeet]

Looking forward to Discord reactions. clap Do you have everything you need to finish the PR?

I still need to figure out how to respond to the redaction of a reaction in Matrix. Unfortunately it looks like I may have to figure out a way to store the records differently so that the event ID of the reaction that comes back in event.redacts can be used to look up the original Matrix event or at least the original Discord message, and it needs to save the emoji used so that it can remove the correct one I believe.

I'll be checking out the code that's in #862 to maybe pull some implementation details from there (hopefully without depdending on that PR since it's still in review I guess)

[mangofeet]

OK, so I got reactions redacting from matrix to discord. Still need to figure out the edge case of the thumbs up, but otherwise it's working as I intended now.

[mangofeet]

Handled the thumbs up exception from Matrix to Discord, but not the other way around yet, not sure if that's strictly necessary to merge this though. It may be better to get this and #862 merged, and then handle any emoji exceptions in a unified manner after the fact.

[TheTechmage]

After reading this if statement, I'm assuming that this is related to the skin-tones? If so, you may want to do proper parsing of those, as more than thumbs up is affected. There's also country flags which use a similar concept.