Log Message:
harfbuzz{,-icu}: update to 2.8.1

Overview of changes leading to 2.8.1
Tuesday, May 4, 2021
====================================
- Subsetter now fully supports GSUB/GPOS/GDEF tables (including variations); as
  such, layout tables are retained by subsetter by default. (Garret Rieger, \ 
Qunxin Liu)
- Build scripts no longer check for FontConfig as HarfBuzz does not use it.
- hb-view supports iTerm2 and kitty inline image protocols (Khaled Hosny),
  it can also use Chafa for terminal graphics if available (Hans Petter Jansson).

Overview of changes leading to 2.8.0
Tuesday, March 16, 2021
====================================
- Shape joining scripts other than Arabic/Syriac using the Universal Shaping Engine.
  Previously these were shaped using the generalized Arabic shaper. (David Corbett)
- Fix regression in shaping of U+0B55 ORIYA SIGN OVERLINE. (David Corbett)
- Update language tags. (David Corbett)
- Variations: reduce error: do not round each interpolated delta. (Just van Rossum)
- Documentation improvements. (Khaled Hosny, Nathan Willis)
- Subsetter improvements: subsets most, if not all, lookup types now. (Garret Rieger,
  Qunxin Liu)
- Fuzzer-found fixes and other improvements when memory failures happen. (Behdad)
- Removed most atomic implementations now that we have C++11 atomic impl. (Behdad)
- General codebase upkeep; using more C++11 features: constexpr constructors, etc.
  (Behdad)