compiler: support ellipsis for append of non-byte slices

NeoVM lacks opcode for array append, thus some
kind of loop is needed for this.

pkg/compiler/slice_test.go

@@ -181,6 +181,23 @@ var sliceTestCases = []testCase{
 			stackitem.NewBigInteger(big.NewInt(5)),
 		},
 	},
+	{
+		"int slice, append slice",
+		`package foo
+			func getByte() byte { return 0x80 }
+			func Main() []int {
+				x := []int{1}
+				y := []int{2, 3}
+				x = append(x, y...)
+				x = append(x, y...)
+				return x
+			}`,
+		[]stackitem.Item{
+			stackitem.Make(1),
+			stackitem.Make(2), stackitem.Make(3),
+			stackitem.Make(2), stackitem.Make(3),
+		},
+	},
 	{
 		"declare compound slice",
 		`package foo