Implement Arabic i18n support

[Razoric480]

Part of #1305 workstream

This will lump in Hebrew a little, in that support for one will add support for the other.

• Add NotoSansArabic as a fallback to our theme fonts
• Get the TranslationManager to differentiate between default inherited and RTL languages and control the layout_direction. This gives us an 80%/20% all on its own.

Identify and fix edge cases where godot's automatic layout direction is not sufficient

• Quizzes are broken (fixed by resetting left/right offsets)

• Godot doesn't automatically switch text alignment - it's still left aligned even in RTL (fixed with a custom richtextlabel with auto-RTL switching)

• Adding arabic as a fallback makes lines take up a lot of vertical space, regardless of whether the language is in arabic or not