This allows partial-instantiating custom Null object for template Lookup<T>.
Before, this had to be handcoded per instantiation. Apparently I missed
adding one for AAT::ankr.lookupTable, so it was getting the wrong (generic)
null for Lookup object, which is wrong and unsafe.
Fixes https://bugs.chromium.org/p/chromium/issues/detail?id=944346
initialize phantom points from metrics from htmx/vmtx & glyf bbox before execution
added source file hb-ot-hmtx-table.cc to call glyf from hmtx/vmtx indirectly & temporarily, workaround a cyclic reference between the two
Re-implemented & repurposed CFF:remap_t as hb_map2_t (moved to hb-ot-layout-common.hh) for two-way mapping for use by index map subsetting.
Hooked up HVAR subsetter through _subset2.
Some renaming in CFF code.
I stumbled over this when trying to upgrade the version of HarfBuzz used by
LibreOffice to 3.2.1 (see <https://gerrit.libreoffice.org/plugins/gitiles/core/
+/b7ddc514bff9bdf682abae537f990aa01dc2c0fb%5E!/> "Upgrade to latest
HarfBuzz 2.3.1"), where building with MSVC 2017 failed like
> c:\cygwin\home\tdf\lode\jenkins\workspace\gerrit_windows\workdir\unpackedtarball\harfbuzz\src\hb-atomic.hh(272): error C2440: 'reinterpret_cast': cannot convert from 'const int *' to 'std::atomic<int> *'
> c:\cygwin\home\tdf\lode\jenkins\workspace\gerrit_windows\workdir\unpackedtarball\harfbuzz\src\hb-atomic.hh(272): note: Conversion loses qualifiers
> c:\cygwin\home\tdf\lode\jenkins\workspace\gerrit_windows\workdir\unpackedtarball\harfbuzz\src\hb-atomic.hh(272): error C2227: left of '->load' must point to class/struct/union/generic type
(see <https://ci.libreoffice.org/job/gerrit_windows/29916/>).
I added all the necessary "const" to make building of HarfBuzz 2.3.1 with
MSVC 2017 succeed for me. There may be more missing at least conceptually.