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/vm/opcodes.c

@@ -1181,6 +1181,8 @@ opfunc_create_implicit_class_constructor (uint8_t opcode, /**< current cbc opcod
 
 /**
  * Set the [[HomeObject]] attribute of the given functon object
+ *
+ * @return void
  */
 extern inline void JERRY_ATTR_ALWAYS_INLINE
 opfunc_set_home_object (ecma_object_t *func_p, /**< function object */
@@ -1636,9 +1638,6 @@ opfunc_collect_private_properties (ecma_value_t constructor, /**< constructor */
  * ClassDefinitionEvaluation environment initialization part
  *
  * See also: ECMAScript v6, 14.5.14
- *
- * @return - ECMA_VALUE_ERROR - if the operation fails
- *           ECMA_VALUE_EMPTY - otherwise
  */
 void
 opfunc_push_class_environment (vm_frame_ctx_t *frame_ctx_p, /**< frame context */