Follow-up to #3702 (CodeRabbit): dimensions are only redrawn when their
recipe changes. Document Color Mode converted their art through the colour
profile, so black became a four-ink C67 M67 Y67 K100 again, and CMYK files
saved before #3702 kept RGB dimension art.
dimension::refresh now also redraws when the document's colour mode
changes. dimension::conform, run when a document is opened or reverted
(Session::add_document, replace_document), redraws a dimension whose art
has colours in the wrong model; one that can't be redrawn keeps its art.
dimension_colours_follow_the_document_colour_model covers RGB to CMYK and
back, and a CMYK document with RGB dimension art being opened. Without the
change it finds C0.67 M0.67 Y0.67 K1 after Document Color Mode.