feat: export (const.)core.v2rayKey (#831)

* comment on.

* rename to V2rayKeyValue

context.go

@@ -9,11 +9,12 @@ import (
 // V2rayKey is the key type of Instance in Context, exported for test.
 type V2rayKey int
 
-const v2rayKey V2rayKey = 1
+// V2rayKeyValue is the key value of Instance in Context, exported for test.
+const V2rayKeyValue V2rayKey = 1
 
 // FromContext returns an Instance from the given context, or nil if the context doesn't contain one.
 func FromContext(ctx context.Context) *Instance {
-	if s, ok := ctx.Value(v2rayKey).(*Instance); ok {
+	if s, ok := ctx.Value(V2rayKeyValue).(*Instance); ok {
 		return s
 	}
 	return nil

functions.go

@@ -16,7 +16,7 @@ import (
 func CreateObject(v *Instance, config interface{}) (interface{}, error) {
 	var ctx context.Context
 	if v != nil {
-		ctx = context.WithValue(v.ctx, v2rayKey, v)
+		ctx = context.WithValue(v.ctx, V2rayKeyValue, v)
 	}
 	return common.CreateObject(ctx, config)
 }