feat: add logc package, support AddGlobalFields for both logc and logx. (#2463)

* feat: add logc package

* feat: add logc, add AddGlobalFields for both logc and logx

* chore: add benchmarks

* chore: add more tests

* chore: simplify globalFields in logx

* chore: remove outdated comments

core/logx/fields.go

@@ -1,11 +1,32 @@
 package logx
 
-import "context"
+import (
+	"context"
+	"sync"
+	"sync/atomic"
+)
 
-var fieldsContextKey contextKey
+var (
+	fieldsContextKey contextKey
+	globalFields     atomic.Value
+	globalFieldsLock sync.Mutex
+)
 
 type contextKey struct{}
 
+// AddGlobalFields adds global fields.
+func AddGlobalFields(fields ...LogField) {
+	globalFieldsLock.Lock()
+	defer globalFieldsLock.Unlock()
+
+	old := globalFields.Load()
+	if old == nil {
+		globalFields.Store(append([]LogField(nil), fields...))
+	} else {
+		globalFields.Store(append(old.([]LogField), fields...))
+	}
+}
+
 // ContextWithFields returns a new context with the given fields.
 func ContextWithFields(ctx context.Context, fields ...LogField) context.Context {
 	if val := ctx.Value(fieldsContextKey); val != nil {