Integrate ICU's bidirectional text handling into BView

[richienyhus]

We need to support people whose language writes text Right-to-Left, but who might want to mention/write something in English or another language that writes text Left-to-Right, therefore creating ​bidirectional text.

As the Locale Kit already uses ICU, we should integrate ICU's ​ubidi class into BView for system wide ​BiDi text support.

This has previously been brought up by Adrian in a ​past mailing list post.

Ubidi can calculate if a text run (chuck of text to be rendered) is Left-to-Right; Right-to-Left; 'Direction Mixed' or 'Direction Neutral' (i.e. an emoji).