Update tileset compose colorspace handling

[ralreegorganon]

Summary

SUMMARY: None

Purpose of change

libvips, used by the tileset compose script, assumes that all files are in the same colorspace. When they're not, it causes issues when they're all composed together.

Describe the solution

Check for an ICC profile, and if it's there, use it to transform the image into sRGB colorspace that libvips assumes images are in.

Describe alternatives you've considered

We could have the script check for this and just complain instead of fix it, but we've generally tried to make it more accepting if it can handle the issue (much as was done for the requirement to have an alpha channel). We can always have it complain in the future.

Testing

Ran the compose both before and after and noted that the sprites missing colors in the before had it in the after.

before

after