[Core Port Req.] NES and SNES from Mesen

There wasn't actually an issue open for this though it had come up in #2146 (re: dropping QuickNes), and also in #1757, in #2364, and on IRC.

If I'm not mistaken, these emulators were written as C++ cores with C#.NET frontends and thus should be easy to integrate into EmuHawk.

Mesen is desired for its accuracy and speed. Its inclusion would probably justify the removal of QuickNes. NesHawk would need to remain even if slightly less accurate because it offers subframe emulation timing (i.e. SubNesHawk). We may end up loading NES roms with either Mesen or NesHawk based on which emulates its mapper more accurately.

The Mesen and Mesen-S projects are on indefinite hiatus, and their repos (SourMesen/Mesen, SourMesen/Mesen-S) have been archived. Were we to fork them, our forks would probably become the focus of its dev community. It's back https://github.com/SourMesen/Mesen2

Mesen-S has an overclocking feature for casual players.

Start by reviewing the prior discussions in issues #2146, #1757, and #2364, then inspect the archived Mesen and Mesen-S repositories and the current Mesen2 project. Determine the scope of integrating the NES and SNES cores into EmuHawk, including the relationship to NesHawk and QuickNes. Done means the required integration work and emulator-selection behavior are defined and implemented.