Add optional AV1 software decoding via dav1d for ExoPlayer (#721)

## Description
Adds the [`dav1d` decoder
module](https://github.com/androidx/media/tree/release/libraries/decoder_av1)
for ExoPlayer as an option. It can be enabled in advanced settings.

Performance will vary between devices.

### Related issues
Closes #103

### Dev notes

As with the ffmpeg module, this one is not required to build the entire
app so it's easier for developers to get started.

This also introduces a customized `DefaultRenderersFactory` for
ExoPlayer, but its largely copied from the super class's implementation.

app/src/main/java/com/github/damontecres/wholphin/preferences/AppPreference.kt

@@ -425,6 +425,18 @@ sealed interface AppPreference<Pref, T> {
                 summary = R.string.force_dovi_profile_7_summary,
             )
 
+        val DecodeAv1 =
+            AppSwitchPreference<AppPreferences>(
+                title = R.string.software_decoding_av1,
+                defaultValue = true,
+                getter = { it.playbackPreferences.overrides.decodeAv1 },
+                setter = { prefs, value ->
+                    prefs.updatePlaybackOverrides { decodeAv1 = value }
+                },
+                summaryOn = R.string.enabled,
+                summaryOff = R.string.disabled,
+            )
+
         val RememberSelectedTab =
             AppSwitchPreference<AppPreferences>(
                 title = R.string.remember_selected_tab,
@@ -1004,6 +1016,7 @@ val advancedPreferences =
                                 AppPreference.DirectPlayAss,
                                 AppPreference.DirectPlayPgs,
                                 AppPreference.DirectPlayDoviProfile7,
+                                AppPreference.DecodeAv1,
                             ),
                         ),
                         ConditionalPreferences(