SPV_KHR_physical_storage_buffer/SPV: Add GL_EXT_buffer_reference_uvec2

Adds uvec2 <-> reference constructor support.
Switches from EXT to KHR for physical_storage_buffer.

Test/spv.bufferhandleUvec2.frag

@@ -0,0 +1,32 @@
+#version 450
+
+#extension GL_EXT_buffer_reference_uvec2 : enable
+
+layout(buffer_reference, std430) buffer blockType {
+    layout(offset = 0)  int a;
+    layout(offset = 4)  int b;
+    layout(offset = 8)  int c;
+    layout(offset = 12) int d;
+    layout(offset = 16) int e;
+};
+
+layout(std430) buffer t2 {
+    blockType f;
+    blockType g;
+} t;
+
+flat in uvec2 h, i;
+
+void main() {
+
+    blockType b1[2] = blockType[2](blockType(h), blockType(i));
+    b1[0].a = b1[1].b;
+    blockType b2 = blockType(h);
+    blockType b3 = blockType(i);
+    b2.a = b3.b;
+    uvec2 j = uvec2(b2);
+    uint carry;
+    j.x = uaddCarry(j.x, 256, carry);
+    j.y += carry;
+    b2 = blockType(j);
+}