Error output should use monospace font

[lrhn]

The error output from the compiler is displayed in a proportional font.
Since it contains lines with "^"s that point into the prior line, that information is lost.
Compare:

main.dart:20:20: Error: Property 'y' cannot be accessed on '({int x, int y})?' because it is potentially null.
Try accessing using ?. instead.
    print((a!.x, a.y, n3: 0)); // ERR
                   ^

with

main.dart:20:20: Error: Property 'y' cannot be accessed on '({int x, int y})?' because it is potentially null.
Try accessing using ?. instead.
    print((a!.x, a.y, n3: 0)); // ERR
                   ^

In the latter, it's possible to see that the ^ is on the y.