Use a more descriptive and distinct field name

It is not immediately clear what maRerun is, besides it can be
confused with regular maRuns.

Change-Id: Idc754a185149a9a4d5e7495b76d8e61f783b42d2
Do proper script itemization with HarfBuzz

This implements http://www.unicode.org/reports/tr24/ by using ICU’s
implementation of it, but since the code in question is private API, I
simply copied the two self-contained files.

This commit is best viewed with --ignore-space-change.

Change-Id: I38c385d4fb6f8a2edc804d48f0aa14df9f0a8b3b
Minor

Change-Id: Iefaa98350c8d6116aa07d4d91be29104a930b8db
Simplify

Change-Id: Id018e985110b024ff107f4221501ece2cf27f5d3