Initial set for Object Spread feature (#890)

src/spread/mult-err-obj-getter-throws.case

src/spread/mult-err-obj-unresolvable.case

src/spread/mult-obj-base.case

src/spread/mult-obj-empty.case

src/spread/mult-obj-ident.case

src/spread/mult-obj-null-empty-undefined.case

src/spread/mult-obj-null.case

src/spread/mult-obj-undefined.case

src/spread/obj-getter-descriptor.case

src/spread/obj-getter-init.case

src/spread/obj-manipulate-outter-obj-in-getter.case

src/spread/obj-mult-spread-getter.case

src/spread/obj-mult-spread.case

src/spread/obj-null.case

src/spread/obj-override-immutable.case

src/spread/obj-overrides-prev-properties.case

src/spread/obj-setter-redef.case

src/spread/obj-skip-non-enumerable.case

src/spread/obj-spread-order.case

src/spread/obj-symbol-property.case