Continue working on realms (#4356)

- Rework symbols to have the same value across realms
- Support realms for native functions
- Support test262
- Use new.target realms for constructing intrinsics

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

docs/02.API-REFERENCE.md

@@ -164,10 +164,10 @@ Container object types:
 
 Well-known symbols:
 
+ - JERRY_SYMBOL_ASYNC_ITERATOR - @@asyncIterator well-known symbol
  - JERRY_SYMBOL_HAS_INSTANCE - @@hasInstance well-known symbol
  - JERRY_SYMBOL_IS_CONCAT_SPREADABLE - @@isConcatSpreadable well-known symbol
  - JERRY_SYMBOL_ITERATOR - @@iterator well-known symbol
- - JERRY_SYMBOL_ASYNC_ITERATOR - @@asyncIterator well-known symbol
  - JERRY_SYMBOL_MATCH - @@match well-known symbol
  - JERRY_SYMBOL_REPLACE - @@replace well-known symbol
  - JERRY_SYMBOL_SEARCH - @@search well-known symbol
@@ -9118,6 +9118,59 @@ main (int argc, char** argv)
 
 - [jerry_construct_object](#jerry_construct_object)
 
+## jerry_set_realm
+
+**Summary**
+
+Replaces the currently active realm (including the global object) with another realm.
+The replacement should be temporary, and the original realm must be restored after
+the tasks are completed. During the replacement, the realm must be referenced
+by the application (i.e. the gc must not reclaim it). This is also true to
+the returned previously active realm, so there is no need to free the value
+after the restoration. The function can only fail if realms are not supported
+or the passed argument is not a realm. In this case the returned exception must
+be freed by [jerry_release_value](#jerry_release_value).
+
+This function is useful to parse a script, create a native function, load a snapshot
+or create an exception in another realm. Each ECMAScript code runs in the realm
+which was active when the code was parsed or loaded regardless of the current realm.
+
+*Notes*:
+- This feature depends on build option (`JERRY_BUILTIN_REALMS`) and can be checked
+  in runtime with the `JERRY_FEATURE_REALM` feature enum value,
+  see: [jerry_is_feature_enabled](#jerry_is_feature_enabled).
+
+**Prototype**
+
+```c
+jerry_value_t
+jerry_set_realm (jerry_value_t realm_value);
+```
+- `realm_value` - the new realm value
+- return
+  - previous realm value - if the passed value is a realm
+  - exception - otherwise
+
+*New in version [[NEXT_RELEASE]]*.
+
+**Example**
+
+```c
+{
+  jerry_value_t realm_value = jerry_create_realm ();
+
+  jerry_value_t old_realm = jerry_set_realm (realm_value);
+
+  ... // usage of the realm
+
+  jerry_set_realm (old_realm);
+}
+```
+
+**See also**
+
+- [jerry_create_realm](#jerry_create_realm)
+
 # ArrayBuffer and TypedArray functions
 
 These APIs all depend on the es.next profile.