Ar: Update MIME type and add magic numbers

Changes:
  Replace application/x-ar with application/x-archive
  ar magic number:  "!<arch>\n"
  deb magic number (Debian 0.93+): "!<arch>\ndebian-binary"

REF:
  https://en.wikipedia.org/wiki/Ar_(Unix)
  https://en.wikipedia.org/wiki/Deb_(file_format)

Test:
  $ touch a && touch b && ar r test.ar a b && cp test.ar test-2.a

  $ xdg-mime query filetype test.ar
  application/x-archive

  $ xdg-mime query filetype dftp_2.2-1.deb
  application/vnd.debian.binary-package

  $ gio info test.ar | grep content-type
  standard::content-type: application/x-archive
  standard::fast-content-type: application/x-archive

  $ gio info dftp_2.2-1.deb | grep content-type
  standard::content-type: application/vnd.debian.binary-package
  standard::fast-content-type: application/vnd.debian.binary-package

  $ hexdump -C -n 8 test.ar
  00000000  21 3c 61 72 63 68 3e 0a                           |!<arch>.|
  00000008

  $ hexdump -C -n 21 dftp_2.2-1.deb
  00000000  21 3c 61 72 63 68 3e 0a  64 65 62 69 61 6e 2d 62  |!<arch>.debian-b|
  00000010  69 6e 61 72 79                                    |inary|
  00000015

  $ ./autogen.sh --prefix=/usr --disable-magic && make && sudo make install

1 files changed, 1 insertions, 1 deletions

diff --git a/data/engrampa.desktop.in.in b/data/engrampa.desktop.in.in
index 26ccf0c..7222ba6 100644
--- a/data/engrampa.desktop.in.in
+++ b/data/engrampa.desktop.in.in
@@ -9,7 +9,7 @@ Terminal=false
 Type=Application
 Icon=engrampa
 Categories=GTK;Utility;Archiving;Compression;
-MimeType=application/x-7z-compressed;application/x-7z-compressed-tar;application/x-ace;application/x-alz;application/x-ar;application/x-arj;application/x-brotli;application/x-brotli-compressed-tar;application/x-bzip;application/x-bzip-compressed-tar;application/x-bzip1;application/x-bzip1-compressed-tar;application/x-cabinet;application/x-cbr;application/x-cbz;application/x-cd-image;application/x-compress;application/x-compressed-tar;application/x-cpio;application/vnd.debian.binary-package;application/x-ear;application/x-ms-dos-executable;application/x-gtar;application/x-gzip;application/x-gzpostscript;application/x-java-archive;application/x-lha;application/x-lzh-compressed;application/x-lrzip;application/x-lrzip-compressed-tar;application/x-lzip;application/x-lzip-compressed-tar;application/x-lzma;application/x-lzma-compressed-tar;application/x-lzop;application/x-lzop-compressed-tar;application/x-ms-wim;application/x-rar;application/x-rar-compressed;application/x-rpm;application/x-rzip;application/x-tar;application/x-tarz;application/x-stuffit;application/x-war;application/x-xz;application/x-xz-compressed-tar;application/x-zip;application/x-zip-compressed;application/x-zoo;application/zip;application/x-archive;application/vnd.ms-cab-compressed;application/zstd;
+MimeType=application/x-7z-compressed;application/x-7z-compressed-tar;application/x-ace;application/x-alz;application/x-arj;application/x-brotli;application/x-brotli-compressed-tar;application/x-bzip;application/x-bzip-compressed-tar;application/x-bzip1;application/x-bzip1-compressed-tar;application/x-cabinet;application/x-cbr;application/x-cbz;application/x-cd-image;application/x-compress;application/x-compressed-tar;application/x-cpio;application/vnd.debian.binary-package;application/x-ear;application/x-ms-dos-executable;application/x-gtar;application/x-gzip;application/x-gzpostscript;application/x-java-archive;application/x-lha;application/x-lzh-compressed;application/x-lrzip;application/x-lrzip-compressed-tar;application/x-lzip;application/x-lzip-compressed-tar;application/x-lzma;application/x-lzma-compressed-tar;application/x-lzop;application/x-lzop-compressed-tar;application/x-ms-wim;application/x-rar;application/x-rar-compressed;application/x-rpm;application/x-rzip;application/x-tar;application/x-tarz;application/x-stuffit;application/x-war;application/x-xz;application/x-xz-compressed-tar;application/x-zip;application/x-zip-compressed;application/x-zoo;application/zip;application/x-archive;application/vnd.ms-cab-compressed;application/zstd;
 Keywords=MATE;archive;manager;compression;
 X-MATE-DocPath=engrampa/engrampa.xml
 X-MATE-Bugzilla-Bugzilla=MATE