BossBar Fixes

[AnOwlBe]

Problem

Fixes & cleans up a few things

Solution

Fixed an issue where you could not delete a keyed boss bar when directly pairing it with the boss bar from key expression resulting in users having to set the boss bar from key to a var then use it
fixed by moving the deletion for keyed bars from BossBarClassInfo to KeyedBossBarClassInfo (not sure why it was in BossBarClassInfo to begin I think I just forgot about it after KeyedBossBarClassInfo was made)

Fixes an issue where an NPE was produced (a Skript internal error) when you tried to create a keyed bossbar and provided an empty var as the key

Fixes some shitty coding conventions I left in BossBarUtils (using c variable names and such)
Changed the SuppressWarnings("unchecked") annotation for ExprSecCreateBossBar to be only for init instead of suppressing needlessly for the entire class

Adds an example of making a keyed boss bar to examples of ExprSecCreateBossBar

Adds to the description of title/name of bossbar telling users that things like shadow sprites or fonts won't work due to a bukkit limitation

Testing Completed

Manual testing completed for the delete boss bar thing it now appears to work fine

Supporting Information

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Completes: none
Related: none
AI assistance: none

[APickledWalrus]

Note to fix gradlew.bat