Fix japanese text rendering with Harfbuzz-NG

In rendering, treat (Hiragana|Katakana|Han)+ sequence like Han.

Task-number: QTBUG-36066
Change-Id: I3b5d2833e73431b07fa0df859b5d716357374cf4
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Clean-up some leftovers

Change-Id: Ia7fb57831af55cf8e0403dbdef2e73f9957fccf7
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Decrease code duplication

Check engine's supported scripts in a single place
and remove unused script parameter from fontEngine().

Change-Id: Ic153803bef519320c370b058e77eac1a4d92afd0
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Get rid of SpecialData::addFormatIndices

and rename SpecialData:: resolvedFormatIndices to resolvedFormats.
Instead, resolvedFormats now stores QTextCharFormat shared copies.

Change-Id: I4a22cb3f5679b980ef52d47e4e1935663dd257ea
Reviewed-by: Lars Knoll <lars.knoll@digia.com>