* vulkan: Programmatically add RoundingModeRTE to all shaders when the device supports it
* use FetchContent to get SPIRV-Headers
* Fetch spirv-headers unconditionally
* remove fetchcontent, rely on installed headers
* fix ubuntu job
* Update docs/build.md
This change combines the rms_norm+mul and rope+view+set_rows fusions to
allow fusing the whole sequence together. This comes up in Qwen3, Bailing,
and some other models.
Jeff Bolz