Slow rendering of type error messages

[sjakobi]

In #1496 (comment) @Gabriel439 described a case of a type error where the rendering of the type context was so slow he ended up turning it off completely (#1482).

However if you use --explain you still get the context, and have to wait.

I think there are at least two things that we can do about this:

• Speed up prettyprinter: changesUponFlattening can be slow quchen/prettyprinter#99

• Increase laziness in the rendered types: Right now we use snip to cut off the middle of the rendered types, keeping only the first and last 20 lines.
  I believe that if we'd limit ourselves to the first lines of the type, and use lazy Text instead of strict Text, we might be able to avoid rendering the full document.

[sjakobi]

Some more, less promising, ideas:

• Replace layoutSmart with layoutPretty

• Skip removeTrailingWhitespace for error messages

[sjakobi]

Hmm, I believe #1556 was a bad move in the context of this issue.

While the type error previously took about 7s for me to finish rendering, it now takes about 8.7s. I believe the additional time is spent rendering the colour codes.

I can revert it if that seems like the better tradeoff.

[Gabriella439]

@sjakobi: It's fine because it only affects the --detailed mode. My reasoning is that users who use --detailed are willing to wait longer to get better output