gl_shader_decompiler: Implement XMAD instruction.

vfs: Make type hierarchy objects classes instead of structs

Makes it consistent with the other VFS interfaces and prevents implicit
construction.

struct should be used when the data type is very simple or otherwise has
no invariants associated with it. Given these are used to form a
hierarchy, class should be used instead.

Fixed invalid cast in loader

cubeb_sink: Protect queue with a mutex

GetAudioDeviceServiceWithRevisionInfo (Used by Bloodstained: Curse of the Moon)

Added GetAudioRendererSampleRate, GetAudioRendererSampleCount & GetAudioRendererMixBufferCount

 hid: Stub DisconnectNpad() 

externals: Update to SDL2-2.0.8.

GL renderer: Pick the streambuffer from citra and use them.

Don't emut copies, especially not for data, which is used once. They just end in a huge GPU overhead.

Please see https://github.com/citra-emu/citra/pull/3666 for more details.

As we're not handling any anything about the revision data for GetAudioDeviceServiceWithRevisionInfo, it's currently marked as stubbed. However for games this shouldn't affect the result. Proper revision info would be more for homebrew.

Prevents clang-format from butchering them.

This is required by ARMS.

gl_shader_decompiler: Fix SetOutputAttributeToRegister empty check.

 CMakeLists: Change MSVC14 variable to MSVC_VERSION

GetAudioRendererSampleRate is set as a "STUB" as a game could check if the sample rate it sent and the sample rate it wants don't match. Just a thought of something which could happen so keeping it as stub for the mean time

Stub UpdateUserPresence

gl_shader_decompiler: Fix GLSL compiler error with KIL instruction.

Needed for Retro City Rampage to go in game

GetMessageForResultStatus takes a u16, not a size_t.

Several Friend service fixes

core: Namespace EmuWindow

gl_rasterizer: Silence implicit truncation warning in SetupShaders()

GPU/Maxwell3D: Implemented an alternative set of blend factors.

RasterizerGL: Ignore invalid/unset vertex attributes.

These are used by nouveau and some games like SMO.