[iOS] sdl2 audio driver does not follow the "Respect Silent Mode" setting

Is there an existing issue for this?

• This is a bug in RetroArch frontend
• I have searched the existing issues

Description

The sdl2 audio driver seems to ignore the "Respect Silent Mode" setting while a core is running. Menu sounds are properly silenced, but the core's audio always plays, regardless if your device's Silent Mode is on or off.

I discovered this while testing #17711 and #18127 which confused me for a bit.

Expected behavior

If "Respect Silent Mode" is on, core audio should be muted if Silent Mode is on. The coreaudio and openal audio drivers behave properly.

Steps to reproduce the bug

1. Turn on "Settings > Audio > Respect Silent Mode" (on by default on iOS).
2. Have sdl2 selected as the audio driver.
3. Load a core.
4. Toggle the silent switch/Silent Mode and observe that the audio is not muted.

Version/Commit

1.21.0 (54af661d95)

Bisect Results

No response

Present in the nightly version

Yes, this is reproduced in the nightly build

Platform & operating system

iOS 18.5

Affected Cores

All

Environment information

No response

Relevant log output

Start with the iOS sdl2 audio driver and compare its handling of the "Respect Silent Mode" setting with the coreaudio and openal drivers. Reproduce the issue using the listed settings and steps, then verify that core audio is muted in Silent Mode when the setting is enabled and remains unaffected when it is disabled.