Changes

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)