Compile a type that came from another module

[onatozmenn]

Follow-up to #882. A call could cross a module boundary and a type could not, so a program that imported a record, a choice, an effect or a handler was refused however plain the call using it was.

A type crosses the same way a function does, and the thing that matters is that it comes out as what the module that declared it built. Two layouts for one record would make a value of it fit neither, so each module's tables gain the names its use lines asked for rather than a copy of the shape. By name and only for what was asked for, so two modules that both declare a Point keep their own.

The checker carries an imported type by module and name rather than by definition, for the same reason a DefId can't cross at all, and the lowering had no arm for that shape. It has one now, and the name is enough because the borrowing above put the right layout under it.

The agreement test reads a field of a record the other module built and matches on a variant of a choice the other module declared, which is what would break if the two sides disagreed on the layout.

Part of #877.

_{Written with AI assistance.}