harfbuzz: upgrade 2.9.0 -> 2.9.1

Final subset API is in place and if no issues are discovered,
it will be the stable subset API of HarfBuzz 3.0.0.
Old API is kept to ease transition, but will be removed in 3.0.0.
Various fuzzer-found bug fixes.
hb_buffer_append() now handles the pre- and post-context which
previously were left unchanged in the destination buffer.
hb-view / hb-shape now accept following new arguments:
--unicodes-before/after: takes a list of hex numbers that represent Unicode
codepoints.
Undeprecated API:
hb_set_invert()

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>