Rename error to proto applying

Author: Pouya Yarandi

Sources/SwiftProtobuf/ProtobufMirror.swift

@@ -133,7 +133,7 @@ public extension ProtobufMirror {
 
 }
 
-public enum MessageModificationError: Error {
+public enum ProtoApplyingError: Error {
   case typeMismatch
   case invalidFieldNumber
 }

Sources/protoc-gen-swift/MessageGenerator.swift

@@ -417,7 +417,7 @@ class MessageGenerator {
       p.print("""
       func valueAs<T>(_ type: T.Type) throws -> T {
         guard let _value = value as? T else {
-          throw \(namer.swiftProtobufModulePrefix)MessageModificationError.typeMismatch
+          throw \(namer.swiftProtobufModulePrefix)ProtoApplyingError.typeMismatch
         }
         return _value
       }
@@ -427,7 +427,7 @@ class MessageGenerator {
       for f in fields {
         f.generateApplying(printer: &p)
       }
-      p.print("default: throw \(namer.swiftProtobufModulePrefix)MessageModificationError.invalidFieldNumber")
+      p.print("default: throw \(namer.swiftProtobufModulePrefix)ProtoApplyingError.invalidFieldNumber")
       p.print("}")
       p.print("return copy")
     }