[cmake] Use list(APPEND instead of string(APPEND for vulkan codegen args
This was causing the shaders to be incorrectly templated because
both the precision argument and the format argument were being treated
as a single argument by argparse and therefore pasted into shaders
incorrectly. In turn this meant that shaders couldn't be compiled
when the precision or format options were turned on.
Fixes #76195
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76196
Approved by: https://github.com/dagitses
