ImageId struct is 8-bytes large and can fit in CPU register. Passing it
by value lets compiler pass it in register instead of forcing to
reference it from memory.
In my tests this brings
[dome park](https://github.com/OpenRCT2/OpenRCT2/files/6134362/dome-export.zip)
benchgfx results from 42.16s down to 41.08s, or by 2.5%.