layers: use generated layer_intercept_proc()

Call layer_intercept_proc() from xglGetProcAddr() in DrawState, MemTracker,
and generated layers.

There should be no functional difference with this change.
diff --git a/.gitignore b/.gitignore
index 09c4b1c..9389c83 100644
--- a/.gitignore
+++ b/.gitignore
@@ -16,6 +16,7 @@
 tests/xglinfo
 layers/xgl_dispatch_table_helper.h
 layers/xgl_enum_string_helper.h
+layers/xgl_generic_intercept_proc_helper.h
 layers/xgl_struct_string_helper.h
 layers/xgl_struct_wrappers.cpp
 layers/xgl_struct_wrappers.h