This is to reflect the UTC decision to change the encoding model of
New Tai Lue from logical to visual to be similar to Thai, Lao, and
Tai Viet: http://www.unicode.org/L2/L2014/14250.htm#141-C26

The visual encoding is already the current practice of encoding New
Tai Lue on the web anyway:
http://www.unicode.org/L2/L2014/14195-newtailue.txt

Fixes behdad/harfbuzz#66.

Looks like Unsicribe responds to the 'mymr' tag by zeroing marks
GDEF_LATE instead of generic-shaper UNICODE_LATE.  Implement that.

Fixes
Bug 81775 - Incorrect Rendering with harfbuzz-ng myanmar unicode
https://bugs.freedesktop.org/show_bug.cgi?id=81775

Micro-test added based on Padauk.

Still needs update to joining table to fully work.

Now default shaper is truly no-op.

No shaper has more than one behavior re this, so no need for a callback.

Not exhaustively tested, but I think I got the intended logic
right.

The logic can perhaps be simplified.  Maybe we should disabled
normalization with this shaper.  Then again, for now focusing on
correctness.

This reverts commit d5bd0590.

The reasoning behind that logic was flawed and made under
a misunderstanding of the original problem, and caused
regressions as reported by Jonathan Kew in thread titled
"tibetan marks" in Oct 2013.  Apparently I have had fixed
the original problem with this commit:

  7e08f125

So, revert the faulty commit and everything seems to be in good
shape.

See:
http://lists.freedesktop.org/archives/harfbuzz/2013-April/003101.html

Both Indic and SEA seem to do it just fine, but SEA is much
simpler.

Rename HB_SCRIPT_CANADIAN_ABORIGINAL to HB_SCRIPT_CANADIAN_SYLLABICS
and a macro for the old name.

Mozilla Bug 873902 - Display Arabic text with diacritics is bad
https://bugzilla.mozilla.org/show_bug.cgi?id=873902

Handles Tai Tham, Cham, and New Tai Lue for now.

Before, we were zeroing advance width of attached marks for
non-Indic scripts, and not doing it for Indic.

We have now three different behaviors, which seem to better
reflect what Uniscribe is doing:

  - For Indic, no explicit zeroing happens whatsoever, which
    is the same as before,

  - For Myanmar, zero advance width of glyphs marked as marks
    *in GDEF*, and do that *before* applying GPOS.  This seems
    to be what the new Win8 Myanmar shaper does,

  - For everything else, zero advance width of glyphs that are
    from General_Category=Mn Unicode characters, and do so
    before applying GPOS.  This seems to be what Uniscribe does
    for Latin at least.

With these changes, positioning of all tests matches for Myanmar,
except for the glitch in Uniscribe not applying 'mark'.  See preivous
commit.

Myanmar failures down from 51% to 0.00204648%!

MYANMAR: 1123860 out of 1123883 tests passed. 23 failed (0.00204648%)

See comments and discussion on the list.

So we can handle Sinhala split matras smartly...  Coming soon.

It's a simple, right-to-left, script.

Seems to produce more coherent results than trying the Indic shaper on
them.  I'm looking at you, Kh-* fonts...

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.

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.

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

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

The merger of normalizer and glyph-mapping broke shapers that
modified text stream.  Unbreak them by adding a new preprocess_text
shaping stage that happens before normalizing/cmap and disallow
setup_mask modification of actual text.

To room for more allocations, coming.

Hookup some Indic data to it.  More to come.

If there is no GPOS, zero mark advances.

If there *is* GPOS and the shaper requests so, zero mark advances for
attached marks.

Fixes regression with Tibetan, where the font has GPOS, and marks a
glyph as mark where it shouldn't get zero advance.

Enabled for all shapers except for Indic.

Add a shaper class struct.

When we removed the separate Hangul shaper, the specific normalization
preference of Hangul was lost.  Fix that.  Also, the Thai shaper was
copied from Hangul, so had the fully-composed normalization behavior,
which was unnecessary.  So, fix that too.

Fixes all Tibetan failures.  All 180k of them!

Merges back Hangul into the default shaper.

In a new callback...  Currently unused by all complex shapers.