Fixes https://github.com/harfbuzz/harfbuzz/issues/1216

New API:
hb_buffer_set_invisible_codepoint()
hb_buffer_get_invisible_codepoint()

hb-shape / hb-view --invisible-codepoint

"Fixes" //github.com/harfbuzz/harfbuzz/issues/1191

If we wrote just this much every day...

Some clang versions define static_assert as a macro apparently, so we cannot
redefine it...

This reverts commit 94bfea0c.
This reverts commit 4e626278.

So we don't accidentally break it again.

Sorry for the noise, downstream custom builders.  Please adjust.

Users don't expect a new reference returned from a get() function.
Indeed, all users of that API I foud where NOT destroying the reference.
Just change the implementations to NOT return a reference.

This applies to the following APIs:
hb_unicode_funcs_get_default()
hb_glib_get_unicode_funcs()
hb_icu_get_unicode_funcs()

Fixes https://github.com/harfbuzz/harfbuzz/issues/1134

Finally, unified!

Towards possibly using Null pool for some nil objects.

Right now only Old Italic is marked as such.

Fixes https://github.com/harfbuzz/harfbuzz/issues/1000

We expect the buffer to have no flags that the reference doesn't...
Meh. Makes MORX tests pass now. Need to better define the behavior.

At any position, if state is not zero, mark unsafe-to-break before,
unless we can reason it safe.

At any position, if there's an action entry for end-of-text, mark
unsafe to break.

Also changes buffer diff impl to allow for flag differences as long
as the buffer glyph flags are superset of reference glyph flags.

With this, all MORX tests pass.

This only counts recursions right now.  Good start.

Hopefully...
Fixes https://github.com/behdad/harfbuzz/issues/429

If buffers are empty, content type should be ignored.

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

I like to have a mode where CONTAINS_NOTDEF and CONTAINS_DOTTEDCIRCLE are not
returned.  Abused a value of -1 for that.  hb-shape now uses it.  Fixes two
of the six tests failing with --verify in test/shaping/run-tests.sh.

New API.

Change hb_buffer_diff to explicitly cast result of abs to unsigned when
comparing with position_fuzz to avoid unsafe signed/unsigned comparions
warnings on windows.

Based on patch from Jonathan Kew.

Needs more cleaning up and documentation.

New API:
hb_buffer_diff_flags_t
hb_buffer_diff()

We break and shape fragments and reconstruct shape result from them.
Remains to compare to original buffer.  Going to add some buffer
comparison API and use here, instead of open-coding.

Ouch!

Makes consumption easier.

We were relying on cluster merges not requiring unsafe flagging because
they get merged.  If cluster level requests no merging, then we flag
unsafe when merge would have happened.

This shouldn't matter.

Always use the algorithm for non-monotone case.  It's more robust.

Not all shapers code is updated to set this properly.
GSUB and Arabic shaper are updated.
GPOS and other shapers are NOT.

Fixes https://github.com/behdad/harfbuzz/issues/224

Fixes https://bugs.chromium.org/p/chromium/issues/detail?id=614647
If allocation fails, we might be leaving junk behind.  At least
clear it up.

Part of https://github.com/behdad/harfbuzz/issues/277

This makes defining HB_NDEBUG much less relevant, to the
point of irrelevance.  Sorry about all the fuss in previous
release!