Escapes the interpolated strings in the ReservedName/InvalidName/
InvalidSpec (and, for the same consumer-string interpolation class,
Codec) Display arms with char::escape_debug so rendered error
messages cannot carry raw control bytes from consumer input —
review 004 item 14's log-forging finding. The error taxonomy
(variants, kinds, match sites, ADR-008 §5) is unchanged; only the
rendered text's hygiene moved. Pinned by
error_display_escapes_consumer_control_chars.