The currently accepted output of `T19361` contains the following puzzling message: ``` • Couldn't match type ‘m’ with ‘Many’ arising from multiplicity of ‘x’ ‘m’ is a rigid type variable bound by the type signature for: f :: forall a. a -> a ``` Where is `m` bound in `forall a. a -> a`? The problem is that it's in fact `forall {m} a. a %m -> a`, but the pretty-printer does not display that type with explicit multiplicities. I am fixing this in !14761 by leveraging the existing infrastructure of `pprWithInvisibleBitsWhen` and `mayLookIdentical` to handle multiplicities (in addition to what it already handles: `RuntimeRep`s and invisible kinds).