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-helpers-value.c

@@ -939,6 +939,8 @@ ecma_copy_value_if_not_object (ecma_value_t value) /**< value description */
 
 /**
  * Increase reference counter of a value if it is an object.
+ *
+ * @return void
  */
 extern inline void JERRY_ATTR_ALWAYS_INLINE
 ecma_ref_if_object (ecma_value_t value) /**< value description */
@@ -951,6 +953,8 @@ ecma_ref_if_object (ecma_value_t value) /**< value description */
 
 /**
  * Decrease reference counter of a value if it is an object.
+ *
+ * @return void
  */
 extern inline void JERRY_ATTR_ALWAYS_INLINE
 ecma_deref_if_object (ecma_value_t value) /**< value description */
@@ -1136,6 +1140,8 @@ ecma_free_value (ecma_value_t value) /**< value description */
  *   faster for direct values since no function call is performed.
  *   It also increases the binary size so it is recommended for
  *   critical code paths only.
+ *
+ * @return void
  */
 extern inline void JERRY_ATTR_ALWAYS_INLINE
 ecma_fast_free_value (ecma_value_t value) /**< value description */
@@ -1160,6 +1166,8 @@ ecma_free_value_if_not_object (ecma_value_t value) /**< value description */
 
 /**
  * Free an ecma-value object
+ *
+ * @return void
  */
 extern inline void JERRY_ATTR_ALWAYS_INLINE
 ecma_free_object (ecma_value_t value) /**< value description */
@@ -1169,6 +1177,8 @@ ecma_free_object (ecma_value_t value) /**< value description */
 
 /**
  * Free an ecma-value number
+ *
+ * @return void
  */
 extern inline void JERRY_ATTR_ALWAYS_INLINE
 ecma_free_number (ecma_value_t value) /**< value description */