More doxygen cleanup (#4480)

* Let doxygen handle NGRAPH_API macro on objects

* More fixes to doxygen config fdile

* Cleanup

* Fix ngraph as a class

* Add missing API

* Fix build error

doc/doxygen/Doxyfile.in

@@ -3,8 +3,8 @@ PROJECT_BRIEF    = "Intel® nGraph™ library"
 
 OUTPUT_DIRECTORY = @CMAKE_CURRENT_BINARY_DIR@
 INPUT            = @CMAKE_SOURCE_DIR@/src
+INCLUDE_PATH     = @CMAKE_SOURCE_DIR@/src
 RECURSIVE        = YES
-EXCLUDE_PATTERNS = json.hpp
 
 USE_MATHJAX      = YES
 
@@ -12,3 +12,18 @@ GENERATE_XML     = YES
 
 WARN_IF_UNDOCUMENTED = @DOXYGEN_WARN_IF_UNDOCUMENTED@
 QUIET                = @DOXYGEN_QUIET@
+
+ENABLE_PREPROCESSING   = YES
+MACRO_EXPANSION        = YES
+EXPAND_ONLY_PREDEF     = YES
+PREDEFINED             = NGRAPH_API= \
+                         NOP_BACKEND_API= \
+                         CPU_BACKEND_API= \
+                         GCPU_BACKEND_API= \
+                         GPU_BACKEND_API= \
+                         INTERPRETER_BACKEND_API= \
+                         PLAID_BACKEND_API= \
+
+EXCLUDE_PATTERNS  = */plaidml/*
+EXCLUDE_PATTERNS += */gpu/*
+EXCLUDE_PATTERNS += */src/contrib/mlir/*

src/ngraph/runtime/executable.hpp

@@ -20,6 +20,7 @@
 
 #include "ngraph/function.hpp"
 #include "ngraph/runtime/performance_counter.hpp"
+#include "ngraph/runtime/tensor.hpp"
 #include "ngraph/shape.hpp"
 #include "ngraph/type/element_type.hpp"
 
@@ -27,7 +28,6 @@ namespace ngraph
 {
     namespace runtime
     {
-        class Tensor;
         class Executable;
     }
 }

src/ngraph/runtime/gcpu/gcpu_backend.hpp

@@ -22,6 +22,7 @@
 #include <string>
 #include <vector>
 
+#include "ngraph/runtime/backend.hpp"
 #include "ngraph/runtime/reference/allreduce.hpp"
 #include "ngraph/runtime/tensor.hpp"
 

src/ngraph/runtime/tensor.hpp

@@ -21,18 +21,12 @@
 
 #include "ngraph/descriptor/layout/tensor_layout.hpp"
 #include "ngraph/descriptor/tensor.hpp"
-#include "ngraph/runtime/backend.hpp"
 #include "ngraph/shape.hpp"
 #include "ngraph/strides.hpp"
 #include "ngraph/type/element_type.hpp"
 
 namespace ngraph
 {
-    namespace descriptor
-    {
-        class Value;
-    }
-
     namespace runtime
     {
         class NGRAPH_API Tensor