(1.16) Optimize and improve enums

[Matyrobbrt]

This PR improves the performance of the methods in the different enums, especially the ones in EnumBestiaryPages:

• new Random()s are replaced with ThreadLocalRandom.current()
• useless Map<Integer, Enum>s are removed, in favour of Enum.values()
• integers are no longer uselessly converted to an enum, and later, converted to their int representation
• the method EnumBestiaryPages#hasAllPages now uses Collection#containsAll(Collection), and works (before the method didn't work, as it returned too early)

ForgeGradle is also updated to 5+.

[AlexModGuy]

has conflicts

[PaintNinja]

Fixed merge conflicts