Show feedback message when downloads index manually invalidated

Closes #9768

app/src/main/java/eu/kanade/presentation/more/settings/screen/SettingsAdvancedScreen.kt

@@ -221,7 +221,10 @@ object SettingsAdvancedScreen : SearchableSettings {
                 Preference.PreferenceItem.TextPreference(
                     title = stringResource(R.string.pref_invalidate_download_cache),
                     subtitle = stringResource(R.string.pref_invalidate_download_cache_summary),
-                    onClick = { Injekt.get<DownloadCache>().invalidateCache() },
+                    onClick = {
+                        Injekt.get<DownloadCache>().invalidateCache()
+                        context.toast(R.string.download_cache_invalidated)
+                    },
                 ),
                 Preference.PreferenceItem.TextPreference(
                     title = stringResource(R.string.pref_clear_database),

i18n/src/main/res/values/strings.xml

@@ -534,6 +534,7 @@
     <string name="pref_auto_clear_chapter_cache">Clear chapter cache on app launch</string>
     <string name="pref_invalidate_download_cache">Invalidate downloads index</string>
     <string name="pref_invalidate_download_cache_summary">Force app to recheck downloaded chapters</string>
+    <string name="download_cache_invalidated">Downloads index invalidated</string>
     <string name="pref_clear_database">Clear database</string>
     <string name="pref_clear_database_summary">Delete history for entries that are not saved in your library</string>
     <string name="clear_database_source_item_count">%1$d non-library entries in database</string>