Added CopyReader to BlobReader and all subclasses

A deep-copy method CopyReader has been added to BlobReader (virtual) and all of its subclasses (override). This should create a second BlobReader to open the same set of data but with an independent read pointer so that it doesn't interfere with any reads done on the original Reader.

As part of this, IOFile has added code to create a deep copy IOFile pointer onto the same file, with code based on the platform in question to find the file ID from the file pointer and open a new one. There has also been a small piece added to FileInfo to enable a deep copy, but its only subclass at this time already had a copy constructor so this was relatively minor.

Source/Core/DiscIO/CompressedBlob.cpp

@@ -74,6 +74,11 @@ CompressedBlobReader::~CompressedBlobReader()
 {
 }
 
+std::unique_ptr<BlobReader> CompressedBlobReader::CopyReader() const
+{
+  return Create(m_file.Duplicate("rb"), m_file_name);
+}
+
 // IMPORTANT: Calling this function invalidates all earlier pointers gotten from this function.
 u64 CompressedBlobReader::GetBlockCompressedSize(u64 block_num) const
 {