[ocaml] add Transitioning.Format module for semantic tags

Makefile.generating

src/libraries/stdlib/transitioning.ml.in

src/libraries/stdlib/transitioning.mli

src/libraries/utils/rich_text.ml

src/libraries/utils/rich_text.mli

src/plugins/gui/pretty_source.ml

src/plugins/gui/wtext.ml

src/plugins/metrics/metrics_acsl.ml

src/plugins/metrics/metrics_base.ml

src/plugins/metrics/metrics_base.mli

src/plugins/metrics/metrics_cilast.ml