meson: rework -Dstandalone-binaries= option

The option is generalized from a simple boolean switch that enables
a fixed list to a list-of-patterns.
The old value works, but is deprecated: -Dstandalone-binaries=true is translated
to -Dstandalone-binaries=repart,report,tmpfiles,sysusers,shutdown.

We could already build all normal executables as .standalone, but the
installation only supported a small fixes subset. This wasn't flexible
enough:
- packagers might want to provide additional standalone binaries then the
  small subset that was already enabled
- but at the same time, whenever new binaries were added to this subset,
  downstream packaging had to be adjusted in sync, at least in the case of
  Fedora, because otherwise we'd get a complaint about unexpected .standalone
  binaries in the temporary install root.
With the new option, downstreams can just specify the binaries that they
want to be installed in the .standalone variant.

As usual with this type of change, the build dir must be reprovisioned.

meson_options.txt

@@ -40,8 +40,9 @@ option('static-libsystemd', type : 'combo',
 option('static-libudev', type : 'combo',
        choices : ['false', 'true', 'pic', 'no-pic'],
        description : 'install a static library for libudev')
-option('standalone-binaries', type : 'boolean', value : false,
-       description : 'also build standalone versions of supported binaries')
+option('standalone-binaries', type : 'string',
+       deprecated : { 'true' : 'repart,report,shutdown,sysusers,tmpfiles', 'false' : '' },
+       description : 'comma-separated list of patterns specifying binaries to install as .standalone')
 option('build-static', type : 'boolean', value : false,
        description : 'build static versions of supported binaries')