Each kittest harness creates its own wgpu/Vulkan instance on first render, and
lavapipe segfaults when one test creates an instance while another renders
(core dump: vkCreateSampler in libvulkan during a concurrent vkCreateInstance).
The batch tripled the rendering tests in editing.rs. editing and content take
the GPU lock view.rs and fill_sign.rs already use. Crashes over default-thread
runs: editing 11/40 before, 0/40 after; content 4/20 before, 0/20 after.
aiongg
b99c774f01