Also renames related CMake variables to match both the Find*FFmpeg* and
variables defined within the file. Fixes odd errors produced by the old
FindFFmpeg.

Citra's FindFFmpeg is slightly modified here: adds Citra's copyright at
the beginning, renames FFmpeg_INCLUDES to FFmpeg_INCLUDE_DIR, disables a
few components in _FFmpeg_ALL_COMPONENTS, and adds the missing avutil
component to the comment above.

Copies FFmpeg libraries that were downloaded during the CMake
configuration. Fixes dynamic linking issues with the MinGW builds.

For Linux, instructs CMake to use the FFmpeg submodule in externals.
This is HEAVILY based on our usage of the late Unicorn.  Minimal change
to MSVC as it uses the yuzu-emu/ext-windows-bin. MinGW now targets the
same ext-windows-bin libraries as MSVC for FFmpeg. Adds FFMPEG_LIBRARIES
to WIN32 and simplifies video_core/CMakeLists.txt a bit.

video_core: host_shaders: Don't pass --quiet to glslangValidator if unavailable

k_affinity_mask: Avoid implicit truncation to bool

This can cause compiler warnings. Instead, we can explicitly add a
boolean expression around it to naturally turn the result into a bool.

key_manager: Create the keys directory if it does not exist

config: Always update handheld config

audren: Disable reverb for the time being

kernel: Rewrite resource limit to be more accurate

acc: Fix error when second user is selected

Avoid overwriting username

settings: Log the cache, config and mod load directories

Prevents CMake from calling `glslangValidator` with `--quiet` when it is
not available, i.e. on older downstream versions from Ubuntu.

hid: Only update motion for npad and prevent over scheduling events

arm_dynarmic_32: Print out CPSR.T on exception

nifm: Stub GetCurrentNetworkProfile and GetCurrentIpConfigInfo

nifm: Fix GetAppletInfo stub

As this is causing issues in a few games, it's best to have it disabled until it's completely implemented

am/IApplicationFunctions: Stub IsGamePlayRecordingSupported

prepo: Stub RequestImmediateTransmission and GetTransmissionStatus

analog_from_button: Fix update_thread.join exception

- Used by Lets Sing 12

- Used by Animal Crossing: New Horizons

- Used by Minecraft Bedrock Edition
- Used by Bloons TD 5

bsd: Fix EventFd stub

Used by RetroArch

bsd: Fix GetSockOpt stub