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.

Previously, we had WBFS and CISO which both returned an upper bound
of the size, and other formats which returned an accurate size. But
now we also have NFS, which returns a lower bound of the size. To
allow VolumeVerifier to make better informed decisions for NFS, let's
use an enum instead of a bool for the type of data size a blob has.

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.

We want to use positional arguments in translatable strings
that have more than one argument so that translators can change
the order of them, but the question is: Should we also use
positional arguments in translatable strings with only one
argument? I think it makes most sense that way, partially
so that translators don't even have to be aware of the
non-positional syntax and partially because "translatable
strings use positional arguments" is an easier rule for us
to remember than "transitional strings which have more than
one argument use positional arguments". But let me know if
you have a different opinion.

Migrates the DiscIO code over to fmt.