Add RTL/bidi support via `direction` and `unicode-bidi`

[FlorianRappl]

Description
The renderer lacks effective RTL/bidi handling; “direction” usage appears limited to flex-direction-related logic.

Scope

• Implement text/inline directionality from direction and unicode-bidi.
• Support right-to-left inline flow and ordering behavior in standard bidi scenarios.
• Ensure alignment and caret/logical ordering dependencies are accounted for where relevant.

Acceptance criteria

• Mixed LTR/RTL sample text renders in expected visual order.
• direction: rtl affects inline layout as expected.
• Tests cover core bidi embedding/override behavior supported by current architecture.