Module Modes_lib.KindSource
Interprets ident as a kind, expanding abbreviations known to the compiler (e.g. mutable_data).
Raises if ident does not correspond to a know layout or kind abbreviation.
Applies the given modifiers mods to the kind k --- produces the kind (k) mod (mods). This can only strengthen the kind, and so will not necessarily set the bounds to be exactly the modifiers provided.