Implement realm object and support realms for built-ins and JS functions (#4354)

- Type for realm objects is introduced (ecma_global_object_t)
- Realm reference is added to built-in objects and ECMAScript functions
- Resolving built-ins, global environments, and scopes require realm object
- Unnecessary global object accesses are removed from the code

Missing: external functions and static snapshot functions have no realm reference

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

tests/jerry/regression-test-issue-2105.js

@@ -51,4 +51,4 @@ try {
 /* Check properties of a */
 assert(Object.keys(a) == "one,two");
 /* Check properties of global object */
-assert(Object.keys(this) == "assert,gc,print,resourceName,a,fail,fail_two");
+assert(Object.keys(this) == "assert,gc,print,resourceName,createRealm,a,fail,fail_two");