[Cmdline] add Filepath parameter

src/kernel_internals/runtime/special_hooks.ml

src/kernel_services/cmdline_parameters/parameter_builder.ml

...kernel_services/cmdline_parameters/parameter_customize.ml

...ernel_services/cmdline_parameters/parameter_customize.mli

src/kernel_services/cmdline_parameters/parameter_sig.mli

src/kernel_services/plugin_entry_points/dynamic.ml

src/kernel_services/plugin_entry_points/dynamic.mli

src/kernel_services/plugin_entry_points/kernel.ml

src/kernel_services/plugin_entry_points/kernel.mli

src/kernel_services/plugin_entry_points/plugin.ml

src/libraries/utils/filepath.ml

src/libraries/utils/filepath.mli

src/plugins/wp/wp_parameters.ml