Reimplement and simplify Hugo's template system

See #13541 for details.

Fixes #13545
Fixes #13515
Closes #7964
Closes #13365
Closes #12988
Closes #4891

common/types/types.go

@@ -28,6 +28,16 @@ type RLocker interface {
 	RUnlock()
 }
 
+type Locker interface {
+	Lock()
+	Unlock()
+}
+
+type RWLocker interface {
+	RLocker
+	Locker
+}
+
 // KeyValue is a interface{} tuple.
 type KeyValue struct {
 	Key   any