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

Test/vk.relaxed.link1.frag

@@ -0,0 +1,28 @@
+#version 460
+
+out vec4 o;
+
+// default uniforms will be gathered into a uniform block
+// final global block will merge uniforms from all linked files
+uniform vec4 a;     // declared in both stages
+uniform vec2 b1;    // declaration order swapped in other stage
+uniform vec2 b2;
+uniform vec4 c1;    // not delcared in other file
+uniform vec4 d;
+
+// final global buffer will berge buffers from all linked files
+layout (binding = 0) uniform atomic_uint counter1;
+layout (binding = 0) uniform atomic_uint counter2;
+
+vec4 foo();
+
+vec4 bar() {
+    uint j = atomicCounterIncrement(counter1) + atomicCounterDecrement(counter2);
+    vec4 v = a + vec4(b1.x, b1.y, b2.x, b2.y) + c1 + d;
+
+    return float(j) * v;
+}
+
+void main() {
+    o = foo() + bar();
+}