MKVToolNix 84.0 “Sleeper”

# Version 84.0 "Sleeper" 2024-04-28

## New features and enhancements

* mkvmerge: added a new file-specific option `--regenerate-track-uids`. When
  used for Matroska files, `mkvmerge` will generate new random track UIDs
  instead of keeping existing track UIDs. This is done automatically when a
  Matroska file was created by MakeMKV.
* mkvmerge: MP4 reader: added support for FLAC in MP4. Implements #3692.
* MKVToolNix GUI: multiplexer: the "Attachments" tab's title will now include
  the total number of attachments (both from source files & to newly
  attach). Implements #3693.
* translations: added a Norwegian Bokmål translation of the programs by Roger
  Knutsen (see `AUTHORS`).

## Bug fixes

* configure: when called with `--disable-gui` the build system still ran the
  check for the GUI libraries & failed if they weren't found. This check is
  now skipped when the option is given. Fixes #3680.
* mkvmerge: several color-related track header properties were parsed into &
  stored as a wrong integer type internally. This could result in wrong values
  being copied when very large values were present in source files, or in
  error messages when very large values were used as command-line parameters.
* MKVToolNix GUI: multiplexer: the keyboard shortcuts from the "modify
  selected tracks" sub-menu didn't work right after opening a file. They only
  started working after opening the "multiplexer" menu. Fixes #3681.

## Build system changes

* Release v8.0.0 of the `fmt` library is now required. If not found, the
  bundled copy will be used.
* A C++20 compatible compiler is now required for several but certainly not
  all C++20 features. g++ v10 & clang++ v10 should suffice.