Roll Harfbuzz to 2.7.0 (c6ca30dc757ff86416d97d358f20080b979b80c9)

[dnfield]

Rolls harfbuzz to 2.7.0, which contains fixes that improve font-subset (and presumably other good things, we hope).

It is expected that this will impact golden tests that render text. /cc @renyou @mehmetf @Piinks

Fixes flutter/flutter#60325

/cc @zanderso @jonahwilliams FYI

[jason-simmons]

This is not building because HarfBuzz 2.7.0 apparently requires choosing an implementation of threading primitives.

Previously we had been using a default fallback implementation (see https://fuchsia.googlesource.com/third_party/harfbuzz/+/f5c000538699a4e40649508a44f41d37035e6c35/src/hb-mutex.hh#104). But that has been removed.

Defining HAVE_PTHREAD should work for Android and Linux. I'm not sure what the best option is for Fuchsia.

[dnfield]

I'm assuming based on https://fuchsia.dev/fuchsia-src/concepts/system/libc?hl=en#pthreads that this usage of pthreads on Fuchsia is OK.

[zanderso]

I'm assuming based on https://fuchsia.dev/fuchsia-src/concepts/system/libc?hl=en#pthreads that this usage of pthreads on Fuchsia is OK.

Maybe @arbreng or @dreveman can confirm.

[dnfield]

May be a moot point. @chinmaygarde pointed out that we don't really need harfbuzz to do any locking, so we can just tell it to not use mutexes.

[dnfield]

License bot finally seems happy.