mkvtoolnix: updated to 74.0.0

Version 74.0.0 "You Oughta Know" 2023-02-12

New features and enhancements

* mkvmerge: SRT handling: added a hack called `--engage
  keep_whitespaces_in_text_subtitles` which disables stripping whitespaces
  from the start & end of each line of SRT entries during muxing.

Bug fixes

* all: Windows: UNC paths of type `\\?\C:\…` are supported again by switching
  back to Boost's file system library instead of using C++17's file system
  library.
* mkvmerge: AVC/H.264 & HEVC/H.265 packetizers: when appending tracks the
  pixel dimensions will be checked & muxing will be aborted if they don't
  match.
* mkvmerge: file type detection: file types that can be detected unambiguously
  by their content (e.g. Matroska, MP4, WAV…) will now preferred in the
  detection order over file types based on their extension. Prevents certain
  cases of mis-detection, e.g. DTS in WAV but with a file name extension of
  `.dts` being detected as the wrong type of DTS.
* mkvmerge: SRT handling: whitespaces will now be stripped from the start &
  the end of each line of each entry, not just from the end of the last
  line.
* mkvextract: SRT extraction: whitespaces will not be stripped from the start
  & end of the whole entry anymore.
* MKVToolNix GUI: multiplexer: when adding multiple files that include certain
  file types (chapters, segment info and tag files) and when the choice where
  to add them is "all files to a single new tab", these certain file types
  will now be added in the newly added tab as well instead of the current tab
  that had already been open.
* build system: fixed compatibility with Ruby 3.2.0 by using `FileTest.exist?`
  instead of `File.exists?`, `Dir.exists?` & `FileTest.exists?` which were
  removed in that release.

Build system changes

* MKVToolNix is now using & requiring Boost's "file system" and "system"
  libraries again instead of C++17's file system library. This is due to gcc's
  library not supporting UNC paths of types `\\?\C:\dir\file.ext`.


(adam)