refactor and cleanup [skip ci]

submodules/Postbox/Sources/FileSize.swift

@@ -0,0 +1,21 @@
+import Foundation
+
+public func fileSize(_ path: String, useTotalFileAllocatedSize: Bool = false) -> Int? {
+    if useTotalFileAllocatedSize {
+        let url = URL(fileURLWithPath: path)
+        if let values = (try? url.resourceValues(forKeys: Set([.isRegularFileKey, .totalFileAllocatedSizeKey]))) {
+            if values.isRegularFile ?? false {
+                if let fileSize = values.totalFileAllocatedSize {
+                    return fileSize
+                }
+            }
+        }
+    }
+    
+    var value = stat()
+    if stat(path, &value) == 0 {
+        return Int(value.st_size)
+    } else {
+        return nil
+    }
+}