refactor: add SolidLocalizedError for keep code unchanged

Author: vvisionnn

FirebaseCore/Internal/Sources/HeartbeatLogging/RingBuffer.swift

@@ -22,13 +22,9 @@ struct RingBuffer<Element>: Sequence {
   private var tailIndex: Array<Element?>.Index
 
   /// Error types for `RingBuffer` operations.
-  enum Error: LocalizedError {
+  enum Error: SolidLocalizedError {
     case outOfBoundsPush(pushIndex: Array<Element?>.Index, endIndex: Array<Element?>.Index)
 
-    var errorDescription: String? {
-      return (errorDescription as String)
-    }
-
     var errorDescription: String {
       switch self {
       case let .outOfBoundsPush(pushIndex, endIndex):
@@ -113,3 +109,16 @@ struct RingBuffer<Element>: Sequence {
 // MARK: - Codable
 
 extension RingBuffer: Codable where Element: Codable {}
+
+
+// MARK: - SolidLocalizedError
+
+protocol SolidLocalizedError: LocalizedError {
+  var errorDescription: String { get }
+}
+
+extension SolidLocalizedError {
+  var errorDescription: String? {
+    (errorDescription as String)
+  }
+}