Log Message:
tex-fontspec{,-doc}: update to 2.8a

* Add `SwashFont` and `BoldSwashFont` features to support LaTeX's
  now-builtin `\textsw` and `\swshape` commands, with matching
  `SwashFeatures` and `BoldSwashFeatures`.
  A simple implementation that has scope to get more complex if need be.
* Remove some legacy code that extended the NFSS in ways that are now
  handled by LaTeX2e natively.
* Long neglected updates through various Github Issues and pull requests.
  Thanks for your patience with the delays.