feat: localize the vocalization in TtsModel

[kevmo314]

NOTE: This doesn't work yet, we will need to figure out how to load the build context outside of a widget context in the tts isolate.

Localize the vocalization in TtsModel to address #1035.

• Import AppLocalizations in lib/models/tts.dart and lib/screens/settings/tts.dart.
• Update getVocalization method in TtsModel to use AppLocalizations for constructing vocalization strings.
• Add BuildContext parameter to getVocalization method.
• Update SystemMessageModel vocalizations to use localized strings.
• Update the sample message in the ElevatedButton in TextToSpeechScreen to use AppLocalizations.
• Add new localization strings for vocalization in lib/l10n/app_en.arb, lib/l10n/app_es.arb, lib/l10n/app_fr.arb, lib/l10n/app_de.arb, and lib/l10n/app_ja.arb.

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For more details, open the Copilot Workspace session.

[kevmo314]

Three steps are necessary here:

1. Resolve the correct locale. This can be done with

final locale = basicLocaleListResolution(WidgetsBinding.instance.platformDispatcher.locales, AppLocalizations.supportedLocales)

https://api.flutter.dev/flutter/widgets/basicLocaleListResolution.html

2. Construct AppLocalizations:

final l10n = lookupAppLocalizations(Locale("en"));

3. Update the AI-gen'd code to take l10n as an argument instead of BuildContext.

[kevmo314]

@SputNikPlop looks good to me