Fix #1081 and improve OptimizedExplosion readability

[lntricate1]

• Moved the check for equal position into the if statement above, to only run when new entities are fetched (optimization)
• Added the condition of being onGround to that check, to fix OptimizedTNT breaks TNT pushing other TNT #1081
• Renamed some variables in doExplosionA to be more readable
• Removed an unnecessary import for java.util.Collections

[altrisi]

Seems to work testing it on top of 23w44a, though there's conflicts now and I have near zero familiarity with this part of the codebase.

Sorry for the long delay!

[lntricate1]

Hello, I've realized this has an edge case where the behavior is non-vanilla (if an entity moves between 2 explosions happening, this code uses the cached values instead of recalculating for the new position). I'll try to fix it within a few days, please don't merge yet!