Upgrade Mednafen core to 1.21.3

Updated to the latest in commits 360f836bdac30fbd024cb4f16d4507899b4e2603, 8abb1a6b206e6a6fd36b5c0c079133541dfbabea, 82127cbb606f00f66925a61534caf145161cf7b3 and fa530428dc168aad7b27794062f9643fe3c41078.

Important: The following fixes must always be reapplied for an update:

https://github.com/OpenEmu/Mednafen-Core/commit/2287440f95e6b9c7743189c4b441417638912f9c (10.11 compat workaround)
https://github.com/OpenEmu/Mednafen-Core/commit/b9cd6ac6a9cb14bd5968f362c98cbc4763d3309a (10.11 compat workaround)
https://github.com/OpenEmu/Mednafen-Core/commit/18a33dc8abe05ab697ab5ff2e1a366c9da00e9fd (PCE multiple-horizontal-resolution frames workaround)

TODO: Analog is still broken, which changed in 1.21.0 Current broken analog code is: https://github.com/OpenEmu/Mednafen-Core/blob/68bcade3e3285d925c78d9b40375d37297d68430/MednafenGameCore.mm#L3416-L3437

Info from Ryphecha:

changed how analog axis and analog button input data is encoded

before, you'd have separate left and right analog axis inputs, 16-bit each, 0-32767. Now you'll just have one input, 16-bit, 0-65535, center at 32768

and analog buttons are 0-65535 now instead of 0-32767

up and left are generally 0, and right and down are generally 65535, except in the case of the throttle controls of the mission sticks and dual mission sticks on the saturn

additionally, this is all described in the various input info struct's in Mednafen https://github.com/OpenEmu/Mednafen-Core/blob/68bcade3e3285d925c78d9b40375d37297d68430/mednafen/git.h, including bit offsets, which we may want to try parsing, and are generally structured as seen here: https://github.com/OpenEmu/Mednafen-Core/blob/68bcade3e3285d925c78d9b40375d37297d68430/mednafen/drivers/input.cpp#L2522-L2538

OpenEmu / Mednafen-Core

Upgrade Mednafen core to 1.21.3 #17