"Fixes" https://bugs.freedesktop.org/show_bug.cgi?id=86300

Based on discussion someone else who had a similar issue, most probably
the user is releasing FT_Face before destructing hb_face_t / hb_font_t.
While that's a client bug, and while we can (and should) use FreeType
refcounting to help avoid that, it happens that we were accessing
the table when we didn't really have to.  Avoid that.

Add hb_ot_layout_language_get_required_feature_index() again, which
is used in Pango.  This was removed in
da132937 in favor of
hb_ot_layout_language_get_required_feature().

API changes:

  - Added hb_ot_layout_language_get_required_feature_index back.

https://bugzilla.mozilla.org/show_bug.cgi?id=986802
Fixes https://github.com/behdad/harfbuzz/pull/39

API Change:

-hb_ot_layout_language_get_required_feature_index
+hb_ot_layout_language_get_required_feature

New API takes an extra pointer argument.  Pass NULL in to get
behavior of previous API.

Reworked by behdad

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

Filter them out when compiling map.

As per Werner's report on the list.

'layout->gsub' may depend on data owned by 'layout->gsub_blob', so it must
be deinitialized before the blob is destroyed.

We were not initializing the digests properly and as a result they were
being initialized to zero, making digest1 to never do any useful work.

Speeds up Amiri shaping significantly.

After the Ngapi hackfest work, we were assuming that fonts
won't use presentation features to choose specific forms
(eg. conjuncts).  As such, we were using auto-joiner behavior
for such features.  It proved to be troublesome as many fonts
used presentation forms ('pres') for example to form conjuncts,
which need to be disabled when a ZWJ is inserted.

Two examples:

	U+0D2F,U+200D,U+0D4D,U+0D2F with kartika.ttf
	U+0995,U+09CD,U+200D,U+09B7 with vrinda.ttf

What we do now is to never do magic to ZWJ during GSUB's main input
match for Indic-style shapers.  Note that backtrack/lookahead are still
matched liberally, as is GPOS.  This seems to be an acceptable
compromise.

As to the bug that initially started this work, that one needs to
be fixed differently:

  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

New numbers:

BENGALI: 353689 out of 354188 tests passed. 499 failed (0.140886%)
DEVANAGARI: 707305 out of 707394 tests passed. 89 failed (0.0125814%)
GUJARATI: 366349 out of 366457 tests passed. 108 failed (0.0294714%)
GURMUKHI: 60706 out of 60747 tests passed. 41 failed (0.067493%)
KANNADA: 951030 out of 951913 tests passed. 883 failed (0.0927606%)
KHMER: 299070 out of 299124 tests passed. 54 failed (0.0180527%)
LAO: 53611 out of 53644 tests passed. 33 failed (0.0615167%)
MALAYALAM: 1048102 out of 1048334 tests passed. 232 failed (0.0221304%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271666 out of 271847 tests passed. 181 failed (0.0665816%)
TAMIL: 1091753 out of 1091754 tests passed. 1 failed (9.15957e-05%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)
TIBETAN: 208469 out of 208469 tests passed. 0 failed (0%)

Not for Arabic, but for Indic-like scripts.  ZWJ/ZWNJ have special
meanings in those scripts, so let font lookups take full control.

This undoes the regression caused by automatic-joiners handling
introduced two commits ago.

We only disable automatic joiner handling for the "basic shaping
features" of Indic, Myanmar, and SEAsian shapers.  The "presentation
forms" and other features are still applied with automatic-joiner
handling.

This change also changes the test suite failure statistics, such that
a few scripts show more "failures".  The most affected is Kannada.
However, upon inspection, we believe that in most, if not all, of the
new failures, we are producing results superior to Uniscribe.  Hard to
count those!

Here's an example of what is fixed by the recent joiner-handling
changes:

  https://bugs.freedesktop.org/show_bug.cgi?id=58714

New numbers, for future reference:

BENGALI: 353892 out of 354188 tests passed. 296 failed (0.0835714%)
DEVANAGARI: 707336 out of 707394 tests passed. 58 failed (0.00819911%)
GUJARATI: 366262 out of 366457 tests passed. 195 failed (0.0532122%)
GURMUKHI: 60706 out of 60747 tests passed. 41 failed (0.067493%)
KANNADA: 950680 out of 951913 tests passed. 1233 failed (0.129529%)
KHMER: 299074 out of 299124 tests passed. 50 failed (0.0167155%)
LAO: 53611 out of 53644 tests passed. 33 failed (0.0615167%)
MALAYALAM: 1047983 out of 1048334 tests passed. 351 failed (0.0334817%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271539 out of 271847 tests passed. 308 failed (0.113299%)
TAMIL: 1091753 out of 1091754 tests passed. 1 failed (9.15957e-05%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)
TIBETAN: 208469 out of 208469 tests passed. 0 failed (0%)

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.

Not sure if this is the most desired behavior.  It's the most easily
defined though.

Previous logic was just wrong.

Looks at alternate location now.

We still don't look for the old incorrect place of the featureParams.
I'll wait till someone actually complains about it...

And add implementation for StylisticSet UINameID.  No API yet.

The old code doesn't work with all fonts, as Khaled has reported.