Fixes https://github.com/behdad/harfbuzz/issues/552

Fixes https://github.com/behdad/harfbuzz/issues/528

Related to https://github.com/behdad/harfbuzz/issues/528

Apparently a base glyph can also become an attached component of a
ligature if the ligature-forming lookup used IgnoreBase.  This was
being confused with a non-first component of a MultipleSubst and
hence not matched for mark-attachment.  Tweak test to fix.

Fixes https://github.com/behdad/harfbuzz/issues/543

Fixes https://github.com/behdad/harfbuzz/issues/551

Followup to 8b2c94c4

Allow matching sequences of marks attached to different ligatures,
as supposedly the base of the subsequent marks were already jumped
over.

New Indic numbers are:

BENGALI: 353725 out of 354188 tests passed. 463 failed (0.130722%)
DEVANAGARI: 707307 out of 707394 tests passed. 87 failed (0.0122987%)
GUJARATI: 366355 out of 366457 tests passed. 102 failed (0.0278341%)
GURMUKHI: 60729 out of 60747 tests passed. 18 failed (0.0296311%)
KANNADA: 951201 out of 951913 tests passed. 712 failed (0.0747968%)
KHMER: 299071 out of 299124 tests passed. 53 failed (0.0177184%)
MALAYALAM: 1048136 out of 1048334 tests passed. 198 failed (0.0188871%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271662 out of 271847 tests passed. 185 failed (0.068053%)
TAMIL: 1091754 out of 1091754 tests passed. 0 failed (0%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)

Before 71c0a142 GURMUKHI used to be at 15,
because Uniscribe seems to allow this character standalone, but that looks
wrong.

If two marks want to ligate and they belong to different components of the
same ligature glyph, and said ligature glyph is to be ignored according to
mark-filtering rules, then allow.

Example Burmese senquence:

  U+1004,U+103A,U+1039,U+101B,U+103D,U+102D

Test font provided by Norbert Lindenberg.

Fixes https://github.com/behdad/harfbuzz/issues/545

Mark it as matra below to allow the sequence U+0A15, U+0A51, U+0A47.
Oh well...

Fixes https://github.com/behdad/harfbuzz/issues/524

Fixes https://github.com/behdad/harfbuzz/issues/525

Update to commit c000ebf79c095a7d58cf90090bde5715592c4834
plus this bug-fix: https://github.com/grigorig/ucdn/issues/18

https://github.com/behdad/harfbuzz/issues/538

Fixes https://github.com/behdad/harfbuzz/issues/538

This is a temporary hack just to avoid incorrect shaping results, pending proper support
for caching shape-plans with variation coordinates.

* Fix missing xscale in rtl graphite unpacking

* Oops didn't need to mess with yscale

Test with, eg.:
$ LC_ALL=fr_FR.utf-8 ./hb-view NotoSansArabic-VF.ttf بهداد --variations wght=1.2

-o, -O, -u, -v, -V

If buffers are empty, content type should be ignored.

This fixes last of the failing tests: fuzzed.tests.  Green again!

Fixes tests/shaping/tests/cluster.tests

Fixes https://github.com/behdad/harfbuzz/issues/154