Fix the types of builtin prototype objects (#3663)

In ES2015 many builtin prototypes are no longer valid instances of their
respective classes. This change updates affected prototypes to be
regular objects as required.

JerryScript-DCO-1.0-Signed-off-by: Dániel Bátyai dbatyai@inf.u-szeged.hu

tests/jerry/es2015/regression-test-issue-3084.js

@@ -12,4 +12,4 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-assert(String.prototype.repeat(1.1) === "");
+assert("".repeat(1.1) === "");