Add checkstyle rule to validate serialization method completeness

[Copilot]

Enforces that classes implementing JsonSerializable or XmlSerializable provide required serialization methods at compile-time via checkstyle.

Changes

• SerializableMethodsCheck - New checkstyle rule validating:

  • JsonSerializable implementations have instance toJson() and static fromJson(JsonReader)
  • XmlSerializable implementations have instance toXml() and static fromXml(XmlReader)

• Configuration - Enabled in all checkstyle configs (track2, clientcore, vnext)

• Tests - Coverage for missing methods, incorrect modifiers, nested classes, and both interfaces

Example violations caught

// Missing static fromJson - checkstyle error
public class Foo implements JsonSerializable<Foo> {
    @Override
    public JsonWriter toJson(JsonWriter writer) { ... }
    // ERROR: Class implementing JsonSerializable must provide a static fromJson method
}

// Non-static fromJson - checkstyle error  
public class Bar implements JsonSerializable<Bar> {
    @Override
    public JsonWriter toJson(JsonWriter writer) { ... }
    
    public Bar fromJson(JsonReader reader) { ... }  
    // ERROR: Must be static
}

Original prompt

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This section details on the original issue you should resolve

<issue_title>[FEATURE REQ] Checkstyle rule to validate serialization methods exist on types that implement JsonSerializable or XmlSerializable</issue_title>
<issue_description>Add a new checkstyle rule to validate the following:

• classes implementing JsonSerializable (in com.azure.json package) have the toJson and fromJson methods.
• classes implementing XmlSerializble (in com.azure.xml package) have the toXml and fromXml methods.

All custom checkstyle rules are implemented here - https://github.com/Azure/azure-sdk-for-java/tree/main/sdk/tools/linting-extensions/src/main/java/io/clientcore/linting/extensions/checkstyle/checks

The new checkstyle rule should be implemented in the same package as the rest of the checkstyle rules and should be enabled for all libraries by default.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [FEATURE REQ] Checkstyle rule to validate serialization methods exist on types that implement JsonSerializable or XmlSerializable #47915

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