Fix explain rendering with Windows EOL

[mbovel]

[test_windows_full]

[som-snytt]

scala> "a\rb\r\nc\nd".split(raw"\R")
val res0: Array[String] = Array(a, b, c, d)

is convenient.

[mbovel]

Nice, I didn't know about it. Thanks!

[mbovel]

@nicolasstucki I found the problem! 🥳 In your last change, you split a string using EOL but its line ends are always encoded with \n even on Windows. So lines do not get the left border there (which was impossible to spot on the CI logs because left borders are anyway stripped there). A quick fix is to use \n instead (or \R as suggested by som-snytt). This PR does that.

Long-term, we might want to use EOL everywhere instead of \n?

[som-snytt]

Just when you thought it was safe to strip left borders: #17783

I used to see line ending problems often on cygwin using scala 2. I began to prefer f"%n" (which just came up recently, as someone joked on discord that it looks like foul language). The other use case is stripMargin which winds up as

"""|text""".stripMargin.linesIterator.mkString(EOL)

where you really want a macro interpolator to automate it.

[nicolasstucki]

Long-term, we might want to use EOL everywhere instead of \n?

@mbovel could you open an issue to track and explain the details that need to be changed?