We were using a specialization constant to size an array inside an
UBO interface block, which caused the crash in the Vulkan driver.
However, this specialization constant was only used to workaround a
Chrome bug on WebGL. Additionally, specialized array size inside blocks
are not fully supported in spirv.
This workaround simply replaces the specialization constant by a
constant on Vulkan.
Fix#6444
185c83dae2