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.

[mrjasonn]

Wouldn't doing ones that fix custom texture mapping break some custom resource packs which are adapted to the fact that they have broken texture mapping? If that is the case, shouldn't we just optimise it and remember to keep them looking the same as vanilla? (the looking same as vanilla should also be for everything in this PR)

[mrjasonn]

And if we are using the attached resource packs in the Mojiras to optimise the models, shouldn't we have a credits thanking them for their work?

[mrjasonn]

...and for the rest (item frames, propagules) nobody will notice the difference and if they do they won't care....

Please just make them look vanilla (I don't mind them looking different if clip in in spectator mode), as people might want them to actually look vanilla and not just ignore the fact it doesn't look vanilla. You have said that fixes for #1316 and #1902 may make this not visible, so please test on top of those commits. If it is harder to see, still best to keep vanilla in my opinion.

[jellysquid3]

And if we are using the attached resource packs in the Mojiras to optimise the models...

As far as I know, this is Muzikbike's original work. If it's not, then we need to know, since we require that all contributions be the submitter's original work...

[jellysquid3]

The changes seem fine to me. The minor details you mentioned are very unlikely to cause issues. But, for us to import these into the repository, each model file should probably have documentation (in the form of a __comment line at least) explaining what changes were made from Vanilla.