Clusters from harfbuzz are indexed from the start of the buffer,
not from the start of the run analyzed. This confuses other parts
of the code that do assume they are from the start of the run.
This means we have RTL support again with ICU 58+. It makes use of:
- ICU for bidi-itemization
- ICU for script-itemization
- OpenTTD for style-itemization
- harfbuzz for shaping
