feat: typed translation generator

[shenlong-tanwen]

Description

Adds a new translation helper with strict typing. The existing translation extension is copied over to the generated file so as to reduce the number of imports required.

// Get translation instance (marks widget for rebuild on locale change)
final t = Translations.of(context);
String a = t.about;

// BuildContext extension shorthand
String b = context.t.about;

// Nested access for nested JSON keys
String c = t.admin.backup_settings;

// Typed parameters extracted from {placeholders}
String d = t.active_count(count: 5);
String e = t.admin.cleared_jobs(job: "thumbnails");

A static non-context accessor is also added to the generated code and can be used with the following syntax. The syntax is intentionally longer to penalise the usage of it

StaticTranslations.instance.uploading_media

[jrasm91]

Very cool