Instance buffer layout is incorrect under WASM

[ProfLander]

• Instances draw, but with incorrect positions
• Instance buffer appears to be excessively padded
• Manually drawing instances 0..64 for each indirect reveals that all the transform data is there,
  but at unexpectedly wide intervals instead of the expected 1-instance-wide
• Experimented with explicitly specifying struct size and alignment, but makes no difference
• Likely some unaccounted-for wgpu limit