[FEATURE] Allow rerolling damage dice

[colekettler]

Is your feature request related to a problem? Please describe.
I'd like to give players the option to reroll individual damage dice to make features like the Savage Attacker origin feat easier to handle.

Describe the solution you'd like
I know this used to be a feature but it was disabled in 3.0.0. I'd like to help with contributing code and fixing it! Was this feature disabled because of lack of time / demand to fix it, or was it disabled for nightmarish and impossible-to-fix-in-the-current-system reasons? Cautionary tales appreciated if it's a waste of time to try to reimplement it.

Describe alternatives you've considered
Rerolling the entire attack and damage is a decent workaround, but it'd be nice to be able to handle it in the original roll.

Additional context
I remember enough JS to be dangerous, happy to help kick in with a fix with a little starter guidance on why the feature was disabled.

[MangoFVTT]

Pre 3.0.0, RSR created its own chat messages which meant I could add identifiers for individual dice and dice rolls that let me target them specifically with a reroll, and meant that rolls were always exactly in the same order that I could control. Post 3.0.0, RSR hooks into the base dnd5e message and changes the HTML around, which means it is dependent on the base system's message contents. There's no full control of rolls and layouts without needing to do a lot of injection. Still technically possible, but much trickier and likely to need maintenance. I think it's doable, but I haven't had the time to give it much more thought than that