regex: remove [deprecated] functions/methods, code clean, add test for regex_base (#8862)

vlib/regex/regex_test.v

@@ -479,7 +479,21 @@ fn test_regex(){
 		}
 
 	}
-	if debug { println("DONE!") }
 
+	if debug { println("DONE!") }
 }
 
+// test regex_base function
+fn test_regex_func(){
+	query    := r"\d\dabcd"
+	test_str := "78abcd" 
+	mut re, re_err, err_pos := regex.regex_base(query)
+	if re_err == regex.compile_ok {
+		start, end := re.match_string(test_str)
+		assert (start == 0) && (end == 6)
+	} else {
+		eprintln("Error in query string in pos ${err_pos}")
+		eprintln("Error: ${re.get_parse_error_string(re_err)}")
+		assert false
+	}
+}