MKVToolNix 80.0 “Roundabout”

# Version 80.0 "Roundabout" 2023-10-29

## New features and enhancements

* MKVToolNix GUI: if the system's locale uses one of the Han scripts, the GUI
  will force Arabic numerals to be used in spin boxes. This prevents Suzhou
  numerals from being used which seems to be the default on Windows systems
  sold in China. Implements #3624.

## Bug fixes

* build system: fixed detection of Qt6 if `clang` is used for compilation on
  Linux. In that case Qt's `qmake` added a `gcc`-specific option that `clang`
  doesn't understand, `-mno-direct-extern-access`. `configure` will now pass
  the parameter `-spec linux-clang` to `qmake` so that it uses the correct
  compiler flags.
* build system: fixed the use of `mktemp` to be more portable to
  e.g. macOS. Fixes #3608.
* mkvmerge: if a video aspect ratio was given with `--aspect-ratio-factor`,
  the code would apply a second factor based on the pixel resolution,
  resulting in much too large values for the `DisplayWidth` element. For
  example, with a pixel resolution of 720x520 & an aspect ratio factor of 1/1
  the result should be 720x520, but instead it was 900x520. Up until release
  76.0 this has only happened when a track order was given (which
  unfortunately includes all invocations with MKVToolNix GUI as it always
  includes the track order). Starting with release 77.0 this has always
  happened due to the automatic sorting of tracks implicitly creating a track
  order, even if none was given.