CoreText does automatic font fallback (AKA "cascading") for  characters
not supported by the requested font, and provides no way to turn it off,
so detect if the returned run uses a font other than the requested one
and fill in the buffer with .notdef glyphs instead of random indices
glyph from a different font.

The spec and Uniscribe don't allow these, but UTN#11
specifically says the sequence U+104B,U+1038 is valid.
As such, allow all "P V" sequences.  There's about
eight sequences that match that structure, but Roozbeh
thinks it's fine to allow all of them.

Test case: U+104B, U+1038

https://bugs.freedesktop.org/show_bug.cgi?id=71947

The spec and Uniscribe treat it as consonant in the grammar, but
it's not in IndicSyllableCategory.txt, so fix up.

Test sequence: U+1004,U+103A,U+1039,U+104E

https://bugs.freedesktop.org/show_bug.cgi?id=71948

This is broken sequence according to OpenType spec, Uniscribe,
and current HarfBuzz implementation.  But Roozbeh says this
is a valid sequence, so allow it.  There are multiple
"(DB As?)?" constructs in the grammar, but Roozbeh thinks only
this one needs changing.

Test case: 1014,1063,103A

Fixes https://bugs.freedesktop.org/show_bug.cgi?id=71949

Based on research into latest SIL and Windows fonts, pulling in
the latest OpenType language tag proposal from Microsoft, and updating
to latest language tags and names from ISO 639.

Tags based on support in Windows 8.1's 'Myanmar Text' font.

Previously we were only setting this in hb_buffer_clear_contents(),
but set_length(0) is a valid way to reinitialize buffer to use with
new text.

Fixes last of scratch alignment warnings in hb-coretext.

Patch from Scott Fleischman.  Warnings were:

harfbuzz/src/hb-font-private.hh:121:42: Implicit conversion loses
integer precision: 'long long' to 'hb_position_t' (aka 'int')
harfbuzz/src/hb-font-private.hh:126:42: Implicit conversion loses
integer precision: 'long long' to 'hb_position_t' (aka 'int')
harfbuzz/src/hb-font-private.hh:400:85: Implicit conversion loses
integer precision: 'long long' to 'hb_position_t' (aka 'int')
harfbuzz/src/hb-ot-layout-common-private.hh:1115:37: Implicit conversion
loses integer precision: 'long long' to 'int'
harfbuzz/src/hb-ft.cc:421:97: Implicit conversion loses integer
precision: 'unsigned long long' to 'int'
harfbuzz/src/hb-ft.cc:422:97: Implicit conversion loses integer
precision: 'unsigned long long' to 'int'

Patch from Jonathan Kew.

Patch from Emil Eklund.

See thread started by Jonathan with subject "an optimization for complex
fonts".

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.

Avoids "deprecated" warnings.

For Javanese (pref_len == 1) only reorder if it didn't ligate.  That's
sensible, and what the spec says.  For other Indic (pref_len > 1)
only reorder if ligated.

Doesn't change any test numbers.

Patch from Jonathan Kew.  "These changes seem to yield a small but
just-about-measurable improvement with old fonts that lack GPOS
kerning."

See:
https://github.com/prezi/harfbuzz-js/pull/1/files#r7032397

Followup from 6e613f33.

Bug 58714 - Kannada u+0cb0 u+200d u+0ccd u+0c95 u+0cbe does not provide
same results as Windows8
https://bugs.freedesktop.org/show_bug.cgi?id=58714

Test with U+0CB0,U+200D,U+0CCD,U+0C95,U+0CBF and tunga.ttf.

Improves some scripts.  Improves Bengali too, but numbers
are up because we produce better results than Uniscribe for some
sequences now.

New numbers:
BENGALI: 353724 out of 354188 tests passed. 464 failed (0.131004%)
DEVANAGARI: 707307 out of 707394 tests passed. 87 failed (0.0122987%)
GUJARATI: 366349 out of 366457 tests passed. 108 failed (0.0294714%)
GURMUKHI: 60732 out of 60747 tests passed. 15 failed (0.0246926%)
KANNADA: 951190 out of 951913 tests passed. 723 failed (0.0759523%)
KHMER: 299070 out of 299124 tests passed. 54 failed (0.0180527%)
MALAYALAM: 1048140 out of 1048334 tests passed. 194 failed (0.0185056%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271662 out of 271847 tests passed. 185 failed (0.068053%)
TAMIL: 1091753 out of 1091754 tests passed. 1 failed (9.15957e-05%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)

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

This seems to generate much better, almost-perfect, positioning for
Arabic as well as Latin above marks.

Test with WinXP times.ttf and U+05D9,U+05B5.

Seems to be working just fine!

Lohit-Punjabi has a upem of 769!  We were losing one unit in our
code, and FreeType is losing another one...  Test with U+0A06.
Has an advance of 854 in the font.  We were producing 852.
Now we do 853, which is what FreeType is telling us.

See comments from caveat!  Seems to work fine.

This is useful for Javanese which has an atomically encoded pre-base
reordering Ra which should only be reordered if it was substituted
by the pref feature.