Track visibility in TypeEqOrigin
A type equality error can arise from a mismatch between *invisible* arguments just as easily as from visible arguments. But we should really prefer printing out errors from visible arguments over invisible ones. Suppose we have a mismatch between `Proxy Int` and `Proxy Maybe`. Would you rather get an error between `Int` and `Maybe`? Or between `*` and `* -> *`? I thought so, too. There is a fair amount of plumbing with this one, but I think it's worth it. This commit introduces a performance regression in test perf/compiler/T5631. The cause of the regression is not the new visibility stuff, directly: it's due to a change from zipWithM to zipWith3M in TcUnify. To my surprise, zipWithM is nicely optimized (it fuses away), but zipWith3M is not. There are other examples of functions that could be made faster, so I've posted a separate ticket, #14037, to track these improvements. For now, I've accepted the small (6.6%) regression.
Showing with 153 additions and 67 deletions