Revert "Revert "GL_ext_vulkan_glsl_relaxed extension support, and cross stage aware IO mapper""

Test/vk.relaxed.errorcheck.frag

@@ -0,0 +1,16 @@
+#version 460
+
+layout (location = 0) in vec4 io;
+
+out vec4 o;
+
+// default uniforms will be gathered into a uniform block
+uniform vec4 a;     // declared in both stages with different types
+
+vec4 foo() {
+    return a;
+}
+
+void main() {
+    o = io + foo();
+}