Update doxygen and fix documentation (#5106)

Update Doxyfile to version 1.9.1

Re-enable doxygen CI checker

Fix some regular comments that should have been doc comments

Document void return types for some inline functions explicitly

Move start of some doxygen groups so they are included always, and not left
out of certain ifdefs

Ignore some doxygen warnings:
    Member (function) is not documented in headers
    Documented empty return type in headers
    Argument has multiple @param documentation sections

JerryScript-DCO-1.0-Signed-off-by: Máté Tokodi mate.tokodi@szteszoftver.hu

jerry-core/ecma/base/ecma-gc.c

@@ -128,6 +128,8 @@ ecma_init_gc_info (ecma_object_t *object_p) /**< object */
 
 /**
  * Increase reference counter of an object
+ *
+ * @return void
  */
 extern inline void JERRY_ATTR_ALWAYS_INLINE
 ecma_ref_object_inline (ecma_object_t *object_p) /**< object */
@@ -153,6 +155,8 @@ ecma_ref_object (ecma_object_t *object_p) /**< object */
 
 /**
  * Decrease reference counter of an object
+ *
+ * @return void
  */
 extern inline void JERRY_ATTR_ALWAYS_INLINE
 ecma_deref_object (ecma_object_t *object_p) /**< object */
@@ -466,6 +470,8 @@ ecma_gc_mark_compiled_code (ecma_value_t script_value) /**< script value */
 
 /**
  * Mark objects referenced by bound function object.
+ *
+ * @return void
  */
 static void JERRY_ATTR_NOINLINE
 ecma_gc_mark_bound_function_object (ecma_object_t *object_p) /**< bound function object */