Mltop.PluginSpecCoq plugins are identified by their OCaml library name (in the Findlib sense)
val repr : t -> string option * stringrepr p returns a pair of legacy_name, lib_name where lib_name is the canoncial library name.
legacy_name may be Some pname for the cases the plugin was specified in Declare ML Module with their legacy name (for example ltac_plugin). This will stop being supported soon and is only here for compatiblity. Note that the name doesn't include the ".cmxs" / ".cma" extension
val pp : t -> string