Add query fonction in ALC_SOFT_system_events unreleased extension (#938)

* feat(ALC_SOFT_system_events): Add alcEventIsSupportedSOFT method in ALC_SOFT_system_events unreleased extension

The purpose of this addition (to my collection) are allow to retrieve which events are supported and if events are fully supported or if some case isn't managed for some reason

For exemple only some backends provide system events:
 * pipewire -> Full support of extension
 * wasapi -> Full support of extension
 * pulseaudio -> Support of add and remove devices events only
 * coreaudio -> Support of default device change only

* feat(ALC_SOFT_system_events): Fix typo in alext.h

Cf following review : https://github.com/kcat/openal-soft/pull/938#discussion_r1404509828

* feat(ALC_SOFT_system_events): Remove ALC_EVENT_NOT_SUPPORTED_SOFT token

Cf following discussions between this comment : https://github.com/kcat/openal-soft/pull/938#issuecomment-1825876452 to this comment : https://github.com/kcat/openal-soft/pull/938#issuecomment-1826419406

1 files changed, 5 insertions, 0 deletions

diff --git a/alc/backends/base.h b/alc/backends/base.h
index a4079fe4..ea3b57a3 100644
--- a/alc/backends/base.h
+++ b/alc/backends/base.h
@@ -11,6 +11,7 @@
 
 #include "core/device.h"
 #include "core/except.h"
+#include "alc/events.h"
 
 
 using uint = unsigned int;
@@ -79,6 +80,10 @@ struct BackendFactory {
 
     virtual bool querySupport(BackendType type) = 0;
 
+    virtual alc::EventSupport queryEventSupport(alc::EventType eventType, BackendType type) {
+        return alc::EventSupport::NoSupport;
+    }
+
     virtual std::string probe(BackendType type) = 0;
 
     virtual BackendPtr createBackend(DeviceBase *device, BackendType type) = 0;