feat: support custom headers for Xray HTTP outbounds (#9690)

* feat: support custom headers for Xray HTTP outbounds

* feat: simplify HTTP outbound headers input

* feat: validate JSON syntax in HTTP headers

  Keep HTTP outbound headers stored as raw text, while validating
  header names and values against RFC 9110/9112 syntax. Support string
  arrays for multi-value headers, reject duplicate JSON header keys, and
  clarify the invalid header JSON message.

* feat: refactor HTTP header parsing into utility

* Simplify code

* Simplify code

* Update CoreConfigV2rayServiceTests.cs

---------

Co-authored-by: 2dust <31833384+2dust@users.noreply.github.com>

v2rayN/ServiceLib/Resx/ResUI.Designer.cs

@@ -149,7 +149,7 @@ namespace ServiceLib.Resx {
                 return ResourceManager.GetString("Downloading", resourceCulture);
             }
         }
-        
+
         /// <summary>
         ///   查找类似 Failed to convert configuration file 的本地化字符串。
         /// </summary>
@@ -330,6 +330,15 @@ namespace ServiceLib.Resx {
             }
         }
         
+        /// <summary>
+        ///   查找类似 Please enter valid HTTP request headers JSON. 的本地化字符串。
+        /// </summary>
+        public static string InvalidHttpOutboundHeaders {
+            get {
+                return ResourceManager.GetString("InvalidHttpOutboundHeaders", resourceCulture);
+            }
+        }
+
         /// <summary>
         ///   查找类似 Invalid address (URL) 的本地化字符串。
         /// </summary>
@@ -3222,6 +3231,15 @@ namespace ServiceLib.Resx {
             }
         }
         
+        /// <summary>
+        ///   查找类似 HTTP headers 的本地化字符串。
+        /// </summary>
+        public static string TbHttpOutboundHeaders {
+            get {
+                return ResourceManager.GetString("TbHttpOutboundHeaders", resourceCulture);
+            }
+        }
+
         /// <summary>
         ///   查找类似 Port hopping interval 的本地化字符串。
         /// </summary>
@@ -4986,6 +5004,15 @@ namespace ServiceLib.Resx {
             }
         }
         
+        /// <summary>
+        ///   查找类似 Custom HTTP outbound request headers as a JSON object with string or string array values. 的本地化字符串。
+        /// </summary>
+        public static string TipHttpOutboundHeaders {
+            get {
+                return ResourceManager.GetString("TipHttpOutboundHeaders", resourceCulture);
+            }
+        }
+
         /// <summary>
         ///   查找类似 *Default value raw 的本地化字符串。
         /// </summary>