meson: use install_symlink() where applicable

Now our baseline of meson is 0.62, hence install_symlink() can be used.

Note, install_symlink() implies install_emptydir() for specified
install_dir. Hence, this also drops several unnecessary
install_emptydir() calls.

Note, the function currently does not support 'relative' and 'force' flags,
so several 'ln -frsT' inline calls cannot be replaced.

src/cryptsetup/meson.build

@@ -33,6 +33,6 @@ executables += [
 ]
 
 # symlink for backwards compatibility after rename
-meson.add_install_script(sh, '-c',
-                         ln_s.format(bindir / 'systemd-cryptsetup',
-                                     libexecdir / 'systemd-cryptsetup'))
+install_symlink('systemd-cryptsetup',
+                pointing_to : libexecdir_to_bin / 'systemd-cryptsetup',
+                install_dir : libexecdir)