Add support for sound backends & some miniaudio changes (#4978)

Miniaudio now runs everything in a separate audio thread - this uses boost::asio's io_context.
Our miniaudio implementation is now also much simplified - it does not use its own resource manager or device. This might end up being stupid if sounds don't work after changing output device or locking or w/e
I've made the sound controller into an interface, meaning we can support multiple sound backends in Chatterino. I've added a Null sound backend that disables all sound. A QMediaPlayer or QSoundEffect or Qt backend could be added.
Miniaudio might idle & disable the device now too, not sure

I've added some unrelated changes in the form of a new setting type, and a new setting page helper function for it, which will hopefully make adding new enum settings easier in the future.
This setting stores its value as a string instead of an int, and uses magic_enum to convert between that string value and its enum value.

src/widgets/settingspages/GeneralPage.cpp

@@ -5,6 +5,7 @@
 #include "common/Version.hpp"
 #include "controllers/hotkeys/HotkeyCategory.hpp"
 #include "controllers/hotkeys/HotkeyController.hpp"
+#include "controllers/sound/ISoundController.hpp"
 #include "providers/twitch/TwitchChannel.hpp"
 #include "providers/twitch/TwitchIrcServer.hpp"
 #include "singletons/Fonts.hpp"
@@ -20,6 +21,7 @@
 #include "widgets/settingspages/GeneralPageView.hpp"
 #include "widgets/splits/SplitInput.hpp"
 
+#include <magic_enum.hpp>
 #include <QDesktopServices>
 #include <QFileDialog>
 #include <QFontDialog>
@@ -1134,6 +1136,14 @@ void GeneralPage::initLayout(GeneralPageView &layout)
         "Show a Send button next to each split input that can be "
         "clicked to send the message");
 
+    auto *soundBackend = layout.addDropdownEnumClass<SoundBackend>(
+        "Sound backend (requires restart)",
+        magic_enum::enum_names<SoundBackend>(), s.soundBackend,
+        "Change this only if you're noticing issues with sound playback on "
+        "your system",
+        {});
+    soundBackend->setMinimumWidth(soundBackend->minimumSizeHint().width());
+
     layout.addStretch();
 
     // invisible element for width