Adds transparent ends to tile color turf decals.

[CRITAWAKETS]

This PR adds in transparent ends to the turf decals that are used to color tiles, aswell as trimlines. This therefore extends them to the edges of the tile.

Very minor change but one that my eyeballs want so, so much.

Example of before and after:

The Meta Armory circles are less lop-sided now:

Example of Meta Bridge:

Is that a red smooth tile that doesn't have weird green ends sticking out of it??

[CRITAWAKETS]

Sadly after testing, this doesn't really work too well. Decals often look like they're "sunken in" compared to other decals because of the shading being obscured and it's likely attempting to work around this problem would cause many more issues.

also thinking byond's broken-ass alpha rendering might have a hand in this, so uh. oops. byond issue!