Add GL_EXT_texture_shadow_lod support

Closes #3302.

Test/spv.ext.texture_shadow_lod.error.frag

@@ -0,0 +1,13 @@
+#version 450
+
+layout(binding = 0) uniform sampler2DArrayShadow s2da;
+
+layout(location = 0) out vec4 c_out;
+
+layout(location = 0) in vec4 tc;
+
+void main()
+{
+    float c = textureLod(s2da, tc, 0);
+    c_out = vec4(c);
+}