Do not show the additional file/errors table when there's 1 file with many errors

[orta]

E.g. this compile ending:

Found 2 errors in 1 file.

Errors  Files
     2 src/index.ts:14

Now shows as:

Found 2 errors in 1 file: src/index.ts:14

[andrewbranch]

Some unit test failures lit up

[DanielRosenwasser]

Unless I'm mistaken, we shouldn't display a line number in this new message.

[orta]

OK, I'm going to merge this as it has all feedback accepted, and I'd like to rebase #47126 on it