HarfBuzz performance problem

[Kohei Yoshida]

Hi there,

This bug

https://bugs.freedesktop.org/show_bug.cgi?id=75665

reveals that our HarfBuzz based text rendering is quite expensive.  I
tried to do what I could on the Calc side to lessen the impact of this
problem.  I've made some improvement, but I've hit my roadblock.

I was wondering if anyone who is more familiar with HarfBuzz could
suggest any good idea on how to improve this further.

Kohei