feat(i18n): add Turkish locale

Complete the contributed translation against the current English source and
register Turkish in the language picker.

Fills the 51 keys the contribution predated, including the whole
downloads.backgroundWarning block that every locale must translate, and
corrects a few contributed strings: "Sesi Kıs" (volume down) for mute,
"Disket" (floppy) for disc, "bitiş hızı" (finishing speed) for bitrate, and a
"Kısayol Ayaıla" typo.

Consolidates #1683 and #1688, which contributed byte-identical files.

Co-authored-by: Omc725 <98108290+Omc725@users.noreply.github.com>

lib/i18n/strings.g.dart

@@ -3,8 +3,8 @@
 /// Source: lib/i18n
 /// To regenerate, run: `dart run slang`
 ///
-/// Locales: 18
-/// Strings: 26759 (1486 per locale)
+/// Locales: 19
+/// Strings: 28256 (1487 per locale)
 
 // coverage:ignore-file
 // ignore_for_file: type=lint, unused_import
@@ -31,6 +31,7 @@ import 'strings_pl.g.dart' deferred as l_pl;
 import 'strings_pt.g.dart' deferred as l_pt;
 import 'strings_ru.g.dart' deferred as l_ru;
 import 'strings_sv.g.dart' deferred as l_sv;
+import 'strings_tr.g.dart' deferred as l_tr;
 import 'strings_zh.g.dart' deferred as l_zh;
 import 'strings_zh_Hant.g.dart' deferred as l_zh_Hant;
 part 'strings_en.g.dart';
@@ -58,6 +59,7 @@ enum AppLocale with BaseAppLocale<AppLocale, Translations> {
 	pt(languageCode: 'pt'),
 	ru(languageCode: 'ru'),
 	sv(languageCode: 'sv'),
+	tr(languageCode: 'tr'),
 	zh(languageCode: 'zh'),
 	zhHant(languageCode: 'zh', scriptCode: 'Hant');
 
@@ -189,6 +191,13 @@ enum AppLocale with BaseAppLocale<AppLocale, Translations> {
 					cardinalResolver: cardinalResolver,
 					ordinalResolver: ordinalResolver,
 				);
+			case AppLocale.tr:
+				await l_tr.loadLibrary();
+				return l_tr.TranslationsTr(
+					overrides: overrides,
+					cardinalResolver: cardinalResolver,
+					ordinalResolver: ordinalResolver,
+				);
 			case AppLocale.zh:
 				await l_zh.loadLibrary();
 				return l_zh.TranslationsZh(
@@ -309,6 +318,12 @@ enum AppLocale with BaseAppLocale<AppLocale, Translations> {
 					cardinalResolver: cardinalResolver,
 					ordinalResolver: ordinalResolver,
 				);
+			case AppLocale.tr:
+				return l_tr.TranslationsTr(
+					overrides: overrides,
+					cardinalResolver: cardinalResolver,
+					ordinalResolver: ordinalResolver,
+				);
 			case AppLocale.zh:
 				return l_zh.TranslationsZh(
 					overrides: overrides,