Add xrepo download to download package source archive files only.

[waruqi]

Download packages to the current directory

ruki-2:tmp ruki$ xrepo download libogg libplist "zlib 1.2.x"
note: download these packages (pass -y to skip confirm)?
in xmake-repo:
  -> libogg v1.3.4
  -> libplist 2.2.0
  -> zlib v1.2.13
please input: y (y/n)

  => download https://gitlab.xiph.org/xiph/ogg/-/archive/v1.3.4/ogg-v1.3.4.tar.gz .. ok
  => download https://github.com/libimobiledevice/libplist/archive/2.2.0.tar.gz .. ok
  => download https://github.com/madler/zlib/archive/v1.2.13.tar.gz .. ok
outputdir: /private/tmp/packages
install packages ok

ruki-2:tmp ruki$ ls -l ./packages/
total 169872
-rw-r--r--  1 ruki  wheel   255911  5  8 21:09 libogg-v1.3.4.tar.gz
-rw-r--r--  1 ruki  wheel   182563  5  8 21:09 libplist-2.2.0.tar.gz
-rw-r--r--  1 ruki  wheel  1556687  5  8 21:09 zlib-v1.2.13.tar.gz

Download packages to the given output directory

ruki-2:tmp ruki$ xrepo download -o /tmp/output libogg libplist "zlib 1.2.x"
note: download these packages (pass -y to skip confirm)?
in xmake-repo:
  -> libogg v1.3.4
  -> libplist 2.2.0
  -> zlib v1.2.13
please input: y (y/n)

  => download https://github.com/libimobiledevice/libplist/archive/2.2.0.tar.gz .. ok
  => download https://github.com/madler/zlib/archive/v1.2.13.tar.gz .. ok
  => download https://gitlab.xiph.org/xiph/ogg/-/archive/v1.3.4/ogg-v1.3.4.tar.gz .. ok
outputdir: /tmp/output
install packages ok