js: make vlib/v/util compile on JS backend (#12660)

vlib/builtin/js/builtin.v

@@ -83,3 +83,9 @@ pub fn error_with_code(message string, code int) IError {
 		code: code
 	}
 }
+
+// free allows for manually freeing memory allocated at the address `ptr`. no-op on JS backend
+[unsafe]
+pub fn free(ptr voidptr) {
+	_ := ptr
+}

vlib/builtin/js/string.js.v

@@ -955,3 +955,23 @@ pub fn tos(jsstr JS.String) string {
 
 	return res
 }
+
+pub fn (s string) compare(a string) int {
+	min_len := if s.len < a.len { s.len } else { a.len }
+	for i in 0 .. min_len {
+		if s[i] < a[i] {
+			return -1
+		}
+		if s[i] > a[i] {
+			return 1
+		}
+	}
+
+	if s.len < a.len {
+		return -1
+	}
+	if s.len > a.len {
+		return 1
+	}
+	return 0
+}

vlib/builtin/js/utf8.js.v

@@ -11,3 +11,7 @@ pub fn utf8_str_visible_length(s string) int {
 pub fn utf8_str_len(s string) int {
 	return s.len
 }
+
+pub fn utf8_char_len(b byte) int {
+	return ((0xe5000000 >> ((b >> 3) & 0x1e)) & 3) + 1
+}