Fix build errors in swift 5.8 and later using any keyword for type-casting to protocols

Author: Pouya Yarandi

Sources/SwiftProtobuf/GetPathDecoder.swift

@@ -299,7 +299,7 @@ struct GetPathDecoder<T: Message>: Decoder {
 
   mutating func decodeExtensionField(
     values: inout ExtensionFieldValueSet,
-    messageType: Message.Type,
+    messageType: any Message.Type,
     fieldNumber: Int
   ) throws {
     preconditionFailure(

Sources/SwiftProtobuf/Message+FieldMask.swift

@@ -109,8 +109,8 @@ extension Message where Self: Equatable, Self: _ProtoNameProviding {
 
 private extension Message {
   init(removingAllFieldsOf message: Self) {
-    if let type = Self.self as? ExtensibleMessage.Type,
-       let extensible = message as? ExtensibleMessage {
+    if let type = Self.self as? any ExtensibleMessage.Type,
+       let extensible = message as? any ExtensibleMessage {
       self = type.init(extensionsOf: extensible) as? Self ?? .init()
     } else {
       self = .init()
@@ -120,7 +120,7 @@ private extension Message {
 }
 
 private extension Message where Self: ExtensibleMessage {
-  init(extensionsOf message: ExtensibleMessage) {
+  init(extensionsOf message: any ExtensibleMessage) {
     self.init()
     _protobuf_extensionFieldValues = message._protobuf_extensionFieldValues
   }

Sources/SwiftProtobuf/SetPathDecoder.swift

@@ -32,7 +32,7 @@ public enum PathDecodingError: Error {
 
 extension Message {
   static func number(for field: String) -> Int? {
-    guard let type = Self.self as? _ProtoNameProviding.Type else {
+    guard let type = Self.self as? any _ProtoNameProviding.Type else {
       return nil
     }
     return type._protobuf_nameMap.number(forJSONName: field)
@@ -371,7 +371,7 @@ struct SetPathDecoder<T: Message>: Decoder {
 
   mutating func decodeExtensionField(
     values: inout ExtensionFieldValueSet,
-    messageType: Message.Type,
+    messageType: any Message.Type,
     fieldNumber: Int
   ) throws {
     preconditionFailure(