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

Test/vk.relaxed.errorcheck.vert

@@ -0,0 +1,15 @@
+#version 460
+
+layout (location = 0) out vec4 io;
+
+// default uniforms will be gathered into a uniform block
+// final global block will merge uniforms from all linked files
+uniform vec2 a;     // declared in both stages with different type
+
+vec4 foo() {
+    return a.xyxy;
+}
+
+void main() {
+    io = foo();
+}