remove decal after collision

[tcm390]

1. add collision time for every decal.
2. If the decal exist more than 1.5 sec, then clean the decalMesh position attribute.
   This is the result:

Webaverse.-.Google.Chrome.2022-04-13.22-15-04.mp4

[alisaad673]

This seems to work fine. But one suggestion here is to Make the decal not disappear suddenly. Instead, if we can keep reducing the opacity of the decal until it disappears? Is it doable?

bandicam.2022-04-14.19-55-18-302.mp4