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.

SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

Panic alerts in DiscIO can potentially be very annoying since
large amounts of them can pop up when loading the game list
if you have some particularly weird files in your game list.

This was a much bigger problem back in 5.0 with its
"Tried to decrypt data from a non-Wii volume" panic alert, but
I figured I would take it all the way and remove the remaining
panic alerts that can show up when loading the game list.

I have exempted uses of ASSERT/ASSERT_MSG since they indicate
a bug in Dolphin rather than a malformed file.

Migrates the DiscIO code over to fmt.