Add deprecated warnings for same-type casts in SyntaxProtocol

- Implement overloads for `is`, `as`, and `cast` methods in SyntaxProtocol to handle same-type conversions.
- Mark these overloaded methods as deprecated with a warning message that the cast will always succeed.
- Update the codebase to eliminate a redundant casts.

Author: Matejkob

Release Notes/510.md

@@ -30,6 +30,11 @@
   - Issue: https://github.com/apple/swift-syntax/issues/2092
   - Pull Request: https://github.com/apple/swift-syntax/pull/2108
 
+- Same-Type Casts 
+  - Description: `is`, `as`, and `cast` overloads on `SyntaxProtocol` with same-type conversions are marked as deprecated. The deprecated methods emit a warning indicating the cast will always succeed.
+  - Issue: https://github.com/apple/swift-syntax/issues/2092
+  - Pull Request: https://github.com/apple/swift-syntax/pull/2108
+  
 ## API-Incompatible Changes
 
 

Sources/SwiftSyntax/Syntax.swift

@@ -213,20 +213,53 @@ public extension SyntaxProtocol {
     return self.as(syntaxType) != nil
   }
 
+  /// Checks if the current syntax node can be cast to its own type.
+  ///
+  /// - Returns: `true` since the node is already of its own type.
+  ///
+  /// - Note: This method overloads the general `is` method and is marked as deprecated to produce a warning,
+  ///         informing the user that the cast will always succeed.
+  @available(*, deprecated, message: "This cast will always succeed")
+  func `is`(_ syntaxType: Self.Type) -> Bool {
+    return true
+  }
+
   /// Attempts to cast the current syntax node to a given specialized syntax type.
   ///
   /// - Returns: An instance of the specialized type, or `nil` if the cast fails.
   func `as`<S: SyntaxProtocol>(_ syntaxType: S.Type) -> S? {
     return S.init(self)
   }
 
+  /// Casts the current syntax node to its own type.
+  ///
+  /// - Returns: The current syntax node.
+  ///
+  /// - Note: This method overloads the general `as` method and is marked as deprecated to produce a warning,
+  ///         informing the user that the cast will always succeed.
+  @available(*, deprecated, message: "This cast will always succeed")
+  func `as`(_ syntaxType: Self.Type) -> Self? {
+    return self
+  }
+
   /// Force-casts the current syntax node to a given specialized syntax type.
   ///
   /// - Returns: An instance of the specialized type.
   /// - Warning: This function will crash if the cast is not possible. Use `as` to safely attempt a cast.
   func cast<S: SyntaxProtocol>(_ syntaxType: S.Type) -> S {
     return self.as(S.self)!
   }
+
+  /// Force-casts the current syntax node to its own type.
+  ///
+  /// - Returns: The current syntax node.
+  ///
+  /// - Note: This method overloads the general `cast` method and is marked as deprecated to produce a warning,
+  ///         informing the user that the cast will always succeed.
+  @available(*, deprecated, message: "This cast will always succeed")
+  func cast(_ syntaxType: Self.Type) -> Self {
+    return self
+  }
 }
 
 // MARK: Modifying