Preventing unicode § from being typed in JE Survival should be a gamerule.

I get the concern that allowing players to type the § character might cause a spamming issue, but removing the feature entirely in JE Survival seems like a drastic measure. If parity with BE is a goal, the feature blocking this should be changed to a gamerule (as typing § is available there), so players who want to allow their server to type cursed text, bold text, etc; can do so.