display entity support (#2469)
* `billboard` -> `EntityPivot`
* `brightness_*` -> `EntityBrightness`
* `EntityPivot` - minor fixes
* `glow_color` -> `EntityGlowColor`
* `width`/`height` -> `EntityCullingWidth/Height`
* `interpolation_delay` > `EntityInterpolationDelay`
* `EntityInterpolationDuration`
* `shadow_radius` -> `EntityShadowRadius`
* `shadow_strength` -> `EntityShadowStrength`
* `transformation_scale` -> `EntityScale`
* `transformation_translation` > `EntityTranslation`
* Better `DisplayEntityData` transformation handling
* `view_range` -> `EntityViewRange`
* `item_transform` -> `EntityDisplay`
* `text_alignment` -> `EntityDisplay`
* `text_line_width` -> `EntityLineWidth`
* `text` -> `EntityText`
* `text_opacity` -> `EntityOpacity`
* `EntityDefaultBackground`
* `text_is_see_through` -> `EntitySeeThrough`
* `text_is_shadowed` -> `EntityTextShadowed`
* Cleanup `EntityDisplayEntityData`
* Fix `EntityGlowColor` typo
* `interpolation_delay` -> `interpolation_start`
* `interpolation_duration` meta fix
* Properly handle signed->unsigned in `EntityOpacity`
* Improve `EntityViewRange` meta
* `EntityCullingWidth/Height` > `EntityWidth/Height`
* Document what values can be interpolated
* Minor `PropertyRegistry` ordering fix
* Minor meta fix
* `DisplayEntityData` - comment out background color
* Meta fixes
* `PaperAPITools#getText` (Spigot): `null` -> `""`
* Minor meta fixes & code cleanup
* `synonyms` and typo fix
* Add interpolation language doc
* Reference interpolation lang in mechs
* Document `opacity` edge-case
* Copypasta fix
* `EntityLeft/RightRotation`
* `left/right_rotation` -> `primary/secondary`
* Revert "`left/right_rotation` -> `primary/secondary`"
This reverts commit bcaafa57fdaa76252903b56d4ac21ae1d9d1b7ce.
* Document `left/right_rotation`
(
commit: 3bbe017)
