Debugging output for "bad application of execConst" should not use show

[byorgey]

Is your feature request related to a problem? Please describe.
Occasionally we encounter a bug that triggers the dreaded "bad application of execConst" error (e.g. #2186, #2068, #977, #211, probably others). Although this always signals a bug in Swarm (typically in the typechecker or CESK machine), and users would ideally never see it, it does occasionally happen.

Recently in #2186 @xsebek reported causing the game to freeze due to what turned out to be a type error in a recursive function (see fix in #2187). After some investigation, my current hypothesis is that it actually encountered a "bad application of execConst" exception, and then froze while trying to print out a massive Env. Calling show on an Env can result in a ton of output, even exponentially much, because we lose sharing --- especially if some of the bindings in the Env are closures which themselves contain Envs, and so on.

Describe the solution you'd like
Ideally, we should put effort into displaying Env values in a better way for debugging purposes, but that can be a different issue. What I am concerned with here is that we simply should not be calling show on anything to generate output that will be shown in error messages.