arrays: add arrays.each, arrays.each_indexed, and tests for them

vlib/arrays/arrays_test.v

@@ -498,3 +498,46 @@ fn test_partition() {
 	assert lower2.len == 0
 	assert upper2.len == 8
 }
+
+fn test_each() {
+	a := [99, 1, 2, 3, 4, 5, 6, 7, 8, 1001]
+	mut control_sum := 0
+	for x in a {
+		control_sum += x
+	}
+	//
+	each(a, fn (x int) {
+		println(x)
+	})
+	mut sum := 0
+	mut psum := &sum
+	each(a, fn [mut psum] (x int) {
+		unsafe {
+			*psum += x
+		}
+	})
+	assert control_sum == sum
+}
+
+fn test_each_indexed() {
+	a := [99, 1, 2, 3, 4, 5, 6, 7, 8, 1001]
+	mut control_sum := 0
+	f := fn (idx int, x int) int {
+		return (idx + 1) * 1000_000 + x
+	}
+	for idx, x in a {
+		control_sum += f(idx, x)
+	}
+	//
+	each_indexed(a, fn (idx int, x int) {
+		println('idx: ${idx}, x: ${x}')
+	})
+	mut sum := 0
+	mut psum := &sum
+	each_indexed(a, fn [mut psum, f] (idx int, x int) {
+		unsafe {
+			*psum += f(idx, x)
+		}
+	})
+	assert control_sum == sum
+}