Related to but distinct from #50246.

While working on code with a custom array type, I reached a method ambiguity, but the possible fix wasn't particularly helpful:

Possible fix, define
  hcat(::Union{…}, ::Union{…}, ::Vararg{…})

I suspect it would be worthwhile to special case pretty printing in the fix section of method ambiguities so that the types are fully expanded.

cc @ararslan