Optimizes player heads by adding a cache

[Zailer43]

Description

This pull request avoids creating RenderType and getting the skin from the skinmanager every time a player head (inventory, block or placed in the armor slot) was rendered, as they are costly and currently took a similar amount of time as rendering the head itself.

Expected changes

Although, in singleplayer this change should not affect almost anything, in servers or maps where there is a high level of detail and many heads are used it should give a slight improvement, and as you can see in the screenshots below, in general it reduces the micro-stutter.

Spark

These spark tests were run for 30 seconds in the world with a chunk of heads. You can see that where before rendering the heads cost 13396ms it now takes 9000ms

dev branch: https://spark.lucko.me/KDvsr25bBC
this pr: https://spark.lucko.me/Tq8Ek2tpsE

Screenshots

A chunk of heads, worst-case scenario

this pr

dev branch

Entities with custom player heads

this pr

dev branch

A chest full of custom heads

this pr

dev branch

Hypixel's worst optimized lobby

this pr

dev branch

[Zailer43]

Apparently there are moments during 1 or 2 frames heads that had the texture loaded stop having it loaded, I don't understand why and then I should investigate this.

It usually happens in rare situations where the inventory has heads and in one frame all of them lose the skin or an entity that has a head during a frame stops having it.

Edit: now that I think about it, I have only seen this bug on one server, I haven't been playing much on others, but as it happens very rarely (maybe once every 4 hours) I haven't reproduced it on other servers or singleplayer.