HW: Convert FileMonitor::Log into a class.

[AdmiralCurtiss]

Removes global state in FileMonitor.cpp.

[JosJuice]

Having to write FileMonitor::FileLogger feels a bit odd. The two names are ostensibly referring to the same thing, and yet they're nested. But that's just a minor complaint. The rest LGTM.

[AdmiralCurtiss]

I mean, not wrong, but we already had the FileMonitor namespace, and it feels a bit dirty to just have a class in the global namespace. Suggestions?

(why do we not have all of our code in a DolphinEmu namespace or something, anyway?)

[dolphin-emu-bot]

FifoCI detected that this change impacts graphical rendering. Here are the behavior differences detected by the system:

• line-width-test on uberogl-lin-radeon: diff

_{^{automated-fifoci-reporter}}

[JosJuice]

Hm... Yeah, I guess using the global namespace isn't great. If you want to keep it the way it is, I'm okay with that.