SDL_CoreAudio: Use correct 7.1 audio configuration

[Danos0100]

At the moment, when receiving an 8 channel stream, sdl is harcoded to use kAudioChannelLayoutTag_MPEG_7_1_A as channel layout. This layout however is not commonly used, as it uses a 'left of center' and a 'right of center' speaker between Front Left and Center/between Front Right and Center.

SDL/src/audio/coreaudio/SDL_coreaudio.m

Line 882 in e79b0ce

layout.mChannelLayoutTag = kAudioChannelLayoutTag_MPEG_7_1_A;

(L R C LFE Ls Rs Lc Rc)
This leads to SDL-apps on iOS/tvOS trying to output 7.1 audio (like steam link for example) to actually play back surround back audio stream on the surround side speakers and the surround side stream on the front left + center and front right + center speakers, while the surround back speakers stay silent. This also applies to virtualized spatial sound when using AirPods and letting apple do the spatialization.

This needs to be changed to
kAudioChannelLayoutTag_WAVE_7_1 (8 channels, L R C LFE Rls Rrs Ls Rs) (this is the same channel order that is used in windows).

SDL3 has the same problem:

SDL/src/audio/coreaudio/SDL_coreaudio.m

Line 781 in f40a530

layout.mChannelLayoutTag = kAudioChannelLayoutTag_MPEG_7_1_A;

(credit goes to @andygrundman for helping me to find out, why moonlight-ios and steam link use the 7.1 front layout)

(also tagging @slouken as this breaks steam link's 7.1 sound on iOS and tvOS currently)

[slouken]

Fixed, thanks!