meson: allow optional static linking of shared code in udev helpers

meson: allow optional static linking of shared code in udev helpers

This makes the helper binaries significantly bigger (in some cases, the final
size depends on link options and optimization level), and is only useful for
distributions which want to provide the option to install udev without systemd.
As the linking is improved, the difference between the columns might shrink,
but it's unlikely that linking libshared statically could ever be more
efficient.

E.g. with -O0, no -flto:
                   (static) (shared)
src/udev/ata_id     999176    85696
src/udev/cdrom_id  1024344   111656
src/udev/collect    990344    81280
src/udev/scsi_id   1023592   115656
src/udev/v4l_id     811736    17744

When linked dynamically, install_rpath must be specified, so add that.