Update to ExtCore 0.8.32 so we can use some new functions in the Choice and Choice.List modules.
Replaced some uses of Choice.bindError + Choice.nestedFailwith with Choice.mapError + nestedFailure. This is effectively the same, but simpler, since Choice.bindError allows an error value to be turned back into a result value, which is not always the behavior we want.
Added some type annotations on functions so the argument types are shown as 'thm' instead of 'Choice<thm0, exn>'.