Scoreboard slots are not case-sensitive

The Bug

Scoreboard display slot names are not case-sensitive, which is inconsistent with item slots, many other arguments, and even scoreboard slots themselves.

To Reproduce

1. /scoreboard objectives setdisplay sidebar

   • ✔ No syntax error.

2. /scoreboard objectives setdisplay SIDEBAR.team.aqua

   • ✔ Reports syntax error.

3. /scoreboard objectives setdisplay SIDEBAR

   • ❌ No syntax error.

Code Analysis

Using yarn's mappings for 1.15.1.

In net/minecraft/scoreboard/Scoreboard#getDisplaySlotId, equalsIgnoreCase is used, instead of simple equals.