Had to do some refactoring to make this happen...

Under uniscribe bug compatibility mode, we still plit them
Uniscrie-style, but Jonathan and I convinced ourselves that there is no
harm doing this the Unicode way.  This change makes that happen, and
unbreaks free Sinhala fonts.

1. If there is any offset (x or y), print out both x and y offsets.

2. Always print out the advance in the major direction of the buffer.
Ie. even for zero-advance glyphs, print a "+0".  This is more intuitive.

Mostly affects Myanmar, but also Tai Tham, Javanese, and Cham.  The
latter three are untested (no fonts!).

Windows 8 adds a Myanmar shaper using the 'mym2' tag.  Route that
through the Indic shaper.  It's still very broken, but at least this
does NOT break old-style Myanmar shaping using the generic shaper.

For Arabic and Indic shapers, if the font doesn't have a script system
for the script, use default shaper.

Make an exception for Arabic script since we have fallback logic for
that one.

Windows 8 added support for Myanmar shaping using the "mym2" script tag,
even though Windows never supported the old "mymr" tag.

To be used in upcoming commits.

...instead of using a hardcoded list of Ra characters.

...instead of using a hardcoded list of Ra characters.

Since it has a couple of left-"matras".

As reported on the list:

I am seeing a similar problem building harfbuzz 0.9.5 with Apple gcc
4.0.1 on OS X 10.5 Leopard:

hb-ot-layout-common-private.hh:406: error: 'struct
OT::CoverageFormat1::Iter' is private
hb-ot-layout-common-private.hh:646: error: within this context
hb-ot-layout-common-private.hh:500: error: 'struct
OT::CoverageFormat2::Iter' is private
hb-ot-layout-common-private.hh:647: error: within this context
make[4]: *** [libharfbuzz_la-hb-ot-layout.lo] Error 1

Also reported as happening with MSVC 2005.

Uniscribe doesn't.  And some fonts abuse this feature to get Indic
shaping working in non-complex applications like Adobe's apps.

No change in numbers:

BENGALI: 353897 out of 354188 tests passed. 291 failed (0.0821598%)
DEVANAGARI: 707337 out of 707394 tests passed. 57 failed (0.00805774%)
GUJARATI: 366440 out of 366457 tests passed. 17 failed (0.00463902%)
GURMUKHI: 60704 out of 60747 tests passed. 43 failed (0.0707854%)
KANNADA: 951046 out of 951913 tests passed. 867 failed (0.0910798%)
KHMER: 299074 out of 299124 tests passed. 50 failed (0.0167155%)
LAO: 53611 out of 53644 tests passed. 33 failed (0.0615167%)
MALAYALAM: 1048011 out of 1048334 tests passed. 323 failed (0.0308108%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271666 out of 271847 tests passed. 181 failed (0.0665816%)
TAMIL: 1091754 out of 1091754 tests passed. 0 failed (0%)
TELUGU: 970557 out of 970573 tests passed. 16 failed (0.00164851%)
TIBETAN: 208469 out of 208469 tests passed. 0 failed (0%)

For U+1880..U+1886 Uniscribe thinks they are non-joining.
For U+1887 Uniscribe thinks it's joining, but looks wrong to me.
For now, match Uniscribe.

For U+1880..U+1886 Uniscribe thinks they are non-joining.
For U+1887 Uniscribe thinks it's joining, but looks wrong to me.

Through the Arabic shaper.  It's similar to Mongolian.

Patch from Jonathan Kew.

Part of fixing:

Mozilla Bug 801410 - avoid inserting dotted-circle for run-initial
Unicode combining characters in "simple" scripts such as Latin

https://bugzilla.mozilla.org/show_bug.cgi?id=801410

We should make it clear that we don't want output buffer in this case,
otherwise buffer->backtrack_len() would be wrong.

That's what the spec says, and what Uniscribe does.