This will assist with finding the source of a panic alert based on logs; before, Common\MsgHandler.cpp:113 (or similar) was always used.

Since it was unused, nonexistent values were used in a few places.  I've replaced them.

They're no longer used.

PR #10066 added functionality to call std::abort when a panic alert occurs; however, that PR only implemented it for MsgAlert and not MsgAlertFmtImpl, meaning that the functionality was not used with PanicAlertFmt (only PanicAlert, which is not used frequently).

Prompted by https://dolphin.ci/#/builders/24/builds/985

A 1-character typo in a recent PR caused FifoCI builds to break
horribly and spew millions of panic alerts until buildbot crashed.

This PR adds a new config option -- defaulting to off -- that allows
Dolphin to abort early on when a panic alert occurs instead of
continuing forever.

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.

Adds an interface that uses fmt under the hood, which is much more
flexible than printf, particularly for localization purposes, given fmt
supports positional formatters in a cross-platform manner out of the box
with no configuration necessary.

Continues the migration of our code over to the fmt logger.

s_msg_handler still seems thread unsafe, not sure if it should be or not