Clean up property existence check inconsistencies (#1860)

`jerry_has_property ()` and `jerry_has_own_property ()` are inconsistent
in that they squash their return value into a `bool` when in fact it is
a `jerry_value_t`, thereby giving the wrong impression that a property
is there when it isn't and encouraging the leaking of `jerry_value_t`s
by disguising them as `bool`s.

Fixes https://github.com/jerryscript-project/jerryscript/issues/1859

JerryScript-DCO-1.0-Signed-off-by: Gabriel Schulhof gabriel.schulhof@intel.com

docs/02.API-REFERENCE.md

@@ -2767,19 +2767,22 @@ jerry_create_undefined (void);
 
 **Summary**
 
-Checks whether the object or it's prototype objects have the given property.
+Checks whether the object or its prototype objects have the given property.
+
+*Note*: Returned value must be freed with [jerry_release_value](#jerry_release_value) when it
+is no longer needed.
 
 **Prototype**
 
 ```c
-bool
+jerry_value_t
 jerry_has_property (const jerry_value_t obj_val,
                     const jerry_value_t prop_name_val);
 ```
 
 - `obj_val` - object value
 - `prop_name_val` - property name
-- return value
+- return value - JavaScript boolean value that evaluates to
   - true, if the property exists
   - false, otherwise
 
@@ -2790,8 +2793,10 @@ jerry_has_property (const jerry_value_t obj_val,
   jerry_value_t global_object = jerry_get_global_object ();
   jerry_value_t prop_name = jerry_create_string ((const jerry_char_t *) "handler_field");
 
-  bool has_prop = jerry_has_property (global_object, prop_name);
+  jerry_value_t has_prop_js = jerry_has_property (global_object, prop_name);
+  bool has_prop = jerry_get_boolean_value (has_prop_js);
 
+  jerry_release_value (has_prop_js);
   jerry_release_value (prop_name);
   jerry_release_value (global_object);
 }
@@ -2809,17 +2814,20 @@ jerry_has_property (const jerry_value_t obj_val,
 
 Checks whether the object has the given property.
 
+*Note*: Returned value must be freed with [jerry_release_value](#jerry_release_value) when it
+is no longer needed.
+
 **Prototype**
 
 ```c
-bool
+jerry_value_t
 jerry_has_own_property (const jerry_value_t obj_val,
                         const jerry_value_t prop_name_val);
 ```
 
 - `obj_val` - object value
 - `prop_name_val` - property name
-- return value
+- return value - JavaScript boolean value that evaluates to
   - true, if the property exists
   - false, otherwise
 
@@ -2830,8 +2838,10 @@ jerry_has_own_property (const jerry_value_t obj_val,
   jerry_value_t global_object = jerry_get_global_object ();
   jerry_value_t prop_name = jerry_create_string ((const jerry_char_t *) "handler_field");
 
-  bool has_prop = jerry_has_own_property (global_object, prop_name);
+  jerry_value_t has_prop_js = jerry_has_own_property (global_object, prop_name);
+  bool has_prop = jerry_get_boolean_value (has_prop_js);
 
+  jerry_release_value (jas_prop_js);
   jerry_release_value (prop_name);
   jerry_release_value (global_object);
 }