chore: avatars lod impostor textures

[pravusjif]

issue: https://app.zenhub.com/workspaces/unity-6047bad476c3c0001942ee91/issues/decentraland/unity-renderer/712

Changed avatars LOD Impostor textures to content-server-fetched body snapshots or pre-generated generic snapshots from a texture atlas when the user snapshot cannot be fetched.

Generic snapshots atlas used:

Testing with bots (generic body snapshot lod impostors from atlas)

1. enter https://play.decentraland.zone/index.html?renderer=urn:decentraland:off-chain:renderer-artifacts:chore/AvatarLODImpostorTextures&ENV=zone&position=91,151&ENABLE_AVATAR_LODS
2. open browser console
3. run clientDebug.InstantiateBotsAtCoords(100, 91.2, 151.2, 36, 50) to instantiate 100 bot in the stadium. It may take a little while to load as the bots collections and wearables are being randomized and loaded.

Screen.Recording.2021-07-23.at.16.16.26.mov

Testing with real users (content-server fetched body snapshot lod impostor)

1. enter https://play.decentraland.zone/index.html?renderer=urn:decentraland:off-chain:renderer-artifacts:chore/AvatarLODImpostorTextures&ENV=org&position=-27,60&ENABLE_AVATAR_LODS
2. Try getting close and far away from the other real users to see their LOD Impostor with their snapshot fetched from the content server. It may be better to test on the realm that has more users in that scene (Explore & Play panel may help for this)

Screen.Recording.2021-07-23.at.17.35.19-2.mov

Known Issues

Currently we have 2 known bugs already tracked in specific issues:

• Weird rotation and Y position of impostors [Fixed]
• Incomplete body parts when transitioning from lod [Fixed]

[github-actions]

After the CI passes:

• This branch can be previewed at https://play.decentraland.zone/index.html?renderer=urn:decentraland:off-chain:renderer-artifacts:chore/AvatarLODImpostorTextures
• Code coverage report: https://renderer-artifacts.decentraland.org/branch-coverage/chore/AvatarLODImpostorTextures

[sandrade-dcl]

I have just found several cases where the avatars are keeping as flat sprite even if I'm near to them. I don't know how to reproduce it, I found it testing in Wonderzone.

[sandrade-dcl]

I found an issue with the LOD sprites. I explain it in the previous comment on this PR.

[D4rWiNSS]

I think we should remove the movement of the sprites in the Y-axis, since it is a bit weird right now, the avatars near you don't move up and down. Other than that it looks good to me! GB!

[pravusjif]

I have just found several cases where the avatars are keeping as flat sprite even if I'm near to them. I don't know how to reproduce it, I found it testing in Wonderzone.

I was able to fix this issue in this same PR

[pravusjif]

Managed to fix the "invisible wearables" bug when unlodding an avatar bug in this same PR

[sandrade-dcl]

I no longer reproduce the bug of some avatars that stayed with the LOD sprite even if we were near of them.

I think we have to improve the transition between LOD sprites and the 3D models of the avatars, we should review the correct distance with the other avatars to activate/deactivate their LODs, and we should resolve the problem of seeing farest avatars moving with the LOD sprite without any animation. But I know itill be workd that we will be contemplating on future steps, so good work, this feature is taking shape! :)