render/vulkan: add Vulkan renderer

This new renderer is implemented with the existing wlr_renderer API
(which is known to be sub-optimal for some operations). It's not
used by default, but users can opt-in by setting WLR_RENDERER=vulkan.

The renderer depends on VK_EXT_image_drm_format_modifier and
VK_EXT_physical_device_drm.

Co-authored-by: Simon Ser <contact@emersion.fr>
Co-authored-by: Jan Beich <jbeich@FreeBSD.org>

render/vulkan/shaders/common.vert

@@ -0,0 +1,25 @@
+#version 450
+
+// we use a mat4 since it uses the same size as mat3 due to
+// alignment. Easier to deal with (tighly-packed) mat4 though.
+layout(push_constant, row_major) uniform UBO {
+	mat4 proj;
+	vec2 uv_offset;
+	vec2 uv_size;
+} data;
+
+layout(location = 0) out vec2 uv;
+
+// 4 outlining points and uv coords
+const vec2[] values = {
+	{0, 0},
+	{1, 0},
+	{1, 1},
+	{0, 1},
+};
+
+void main() {
+	vec2 pos = values[gl_VertexIndex % 4];
+	uv = data.uv_offset + pos * data.uv_size;
+	gl_Position = data.proj * vec4(pos, 0.0, 1.0);
+}