Add Brazilian Portuguese (pt_BR) translation (#2769)

- Created strings_pt_BR.arb with complete Brazilian Portuguese translation
- Added pt_BR to language_service.dart (supportedLocales and localeCountryCode)
- Added pt_BR to translation_constants.dart
- All 1172 strings translated to Brazilian Portuguese

Co-authored-by: Omar Hatem <omarh.ismail1@gmail.com>

lib/entities/language_service.dart

@@ -15,6 +15,7 @@ class LanguageService {
     'nl': 'Nederlands (Dutch)',
     'pl': 'Polski (Polish)',
     'pt': 'Português (Portuguese)',
+    'pt_BR': 'Português Brasileiro (Brazilian Portuguese)',
     'ru': 'Русский (Russian)',
     'uk': 'Українська (Ukrainian)',
     'zh': '简体中文 (Chinese Simplified)',
@@ -48,6 +49,7 @@ class LanguageService {
     'nl': 'nld',
     'pl': 'pol',
     'pt': 'prt',
+    'pt_BR': 'bra',
     'ru': 'rus',
     'uk': 'ukr',
     'zh': 'chn',