xgl: Add new resource type for textures

This change modifies xgl.h to include a new descriptor set
slot type for textures, distinct from resources:

    XGL_SLOT_SHADER_TEXTURE_RESOURCE

Buffers continue to use:

    XGL_SLOT_SHADER_RESOURCE

The ordering of their inclusion in binding tables entries is
important: textures must come before buffers.  This is how
the compiler expects them to be laid out.
diff --git a/include/xgl.h b/include/xgl.h
index 52a5f80..f28aa22 100644
--- a/include/xgl.h
+++ b/include/xgl.h
@@ -288,8 +288,13 @@
     XGL_SLOT_SHADER_SAMPLER                                 = 0x00000003,
     XGL_SLOT_NEXT_DESCRIPTOR_SET                            = 0x00000004,
 
+    // LUNARG CHANGE BEGIN - differentiate between textures and buffers
+    XGL_SLOT_SHADER_TEXTURE_RESOURCE                        = 0x00000005,
+
     XGL_DESCRIPTOR_SET_SLOT_TYPE_BEGIN_RANGE                = XGL_SLOT_UNUSED,
-    XGL_DESCRIPTOR_SET_SLOT_TYPE_END_RANGE                  = XGL_SLOT_NEXT_DESCRIPTOR_SET,
+    XGL_DESCRIPTOR_SET_SLOT_TYPE_END_RANGE                  = XGL_SLOT_SHADER_TEXTURE_RESOURCE,
+    // LUNARG CHANGE END
+
     XGL_NUM_DESCRIPTOR_SET_SLOT_TYPE                        = (XGL_DESCRIPTOR_SET_SLOT_TYPE_END_RANGE - XGL_DESCRIPTOR_SET_SLOT_TYPE_BEGIN_RANGE + 1),
     XGL_MAX_ENUM(_XGL_DESCRIPTOR_SET_SLOT_TYPE)
 } XGL_DESCRIPTOR_SET_SLOT_TYPE;