Cannot generate localization files 🐛

[Matej-Hlatky]

Describe the bug

Recently added "Urdu" language in #832 breaks localization generation and possibility to modify existing or adding new languages.

To Reproduce
Steps to reproduce the behavior:

1. Run flutter gen-l10n command
2. See error below:

The arb file your_path/fluent_ui/lib/l10n/intl_ur.arb has the following formatting issue:
FormatException: Control character in string (at line 5, character 29)
  "searchLabel": "تلاش کریں,

Expected behavior
Can ran flutter gen-l10n command without issues to generate Dart localization files.

Additional context
The "searchLabel" value is not properly closed - see

fluent_ui/lib/l10n/intl_ur.arb

Line 5 in b7d453e

"searchLabel": "تلاش کریں,

Then, also generated fluent_localizations_ur.dart file contains english values, instead of translated ones - see:

fluent_ui/lib/l10n/generated/fluent_localizations_ur.dart

Line 14 in b7d453e

String get searchLabel => 'Search';