Optimizations to vanilla block models

[muzikbike]

Fixes #2460.

Models optimized so far:

• Stairs (straight and inner)
• Hoppers (down and horizontal)
• Composter
• Chorus flower
• Turtle eggs of stack size 4
• Candle cakes
• Anvil
• Beacon
• Item frame, with or without map
• Hanging lantern
• Hanging mangrove propagule

Models I'm still to do:

• Dragon egg
• Flower pots and potted objects
• Cauldron

See #2460 for explanations of these optimizations as well as performance comparisons.