Support regex matching with attr (#2258)

* Support regex matching with attr

* Add test case

* Optimizing regex parsing at core start

* simpliy

app/router/config.go

@@ -1,6 +1,7 @@
 package router
 
 import (
+	"regexp"
 	"strings"
 
 	"github.com/xtls/xray-core/common/net"
@@ -145,9 +146,9 @@ func (rr *RoutingRule) BuildCondition() (Condition, error) {
 	}
 
 	if len(rr.Attributes) > 0 {
-		configuredKeys := make(map[string]string)
+		configuredKeys := make(map[string]*regexp.Regexp)
 		for key, value := range rr.Attributes {
-			configuredKeys[strings.ToLower(key)] = strings.ToLower(value)
+			configuredKeys[strings.ToLower(key)] = regexp.MustCompile(value)
 		}
 		conds.Add(&AttributeMatcher{configuredKeys})
 	}