Reword "All" source/ext lang to "Multi" (#7895)

* Add "multi" as a recognized source/ext lang

* Review Changes

app/src/main/java/eu/kanade/tachiyomi/util/system/LocaleHelper.kt

@@ -19,7 +19,7 @@ object LocaleHelper {
             SourcesPresenter.LAST_USED_KEY -> context.getString(R.string.last_used_source)
             SourcesPresenter.PINNED_KEY -> context.getString(R.string.pinned_sources)
             "other" -> context.getString(R.string.other_source)
-            "all" -> context.getString(R.string.all_lang)
+            "all" -> context.getString(R.string.multi_lang)
             else -> getDisplayName(lang)
         }
     }

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

@@ -257,7 +257,7 @@
     <string name="exclude">Exclude: %s</string>
 
       <!-- Extension section -->
-    <string name="all_lang">All</string>
+    <string name="multi_lang">Multi</string>
     <string name="ext_updates_pending">Updates pending</string>
     <string name="ext_update">Update</string>
     <string name="ext_update_all">Update all</string>