feat: handle \r on all operating systems in IO.FS.lines (#4973)

Closes: #4573

src/Init/System/IO.lean

@@ -496,7 +496,7 @@ partial def lines (fname : FilePath) : IO (Array String) := do
       pure lines
     else if line.back == '\n' then
       let line := line.dropRight 1
-      let line := if System.Platform.isWindows && line.back == '\x0d' then line.dropRight 1 else line
+      let line := if line.back == '\r' then line.dropRight 1 else line
       read <| lines.push line
     else
       pure <| lines.push line

tests/lean/run/4573.lean

@@ -0,0 +1,12 @@
+def test : IO Unit := do
+  let tmpFile := "4573.tmp"
+  let baseLines := #["foo", "bar", "foobar"]
+  let content := baseLines[0] ++ "\r\n" ++ baseLines[1] ++ "\n" ++ baseLines[2]
+  IO.FS.writeFile tmpFile content
+  let readLines ← IO.FS.lines tmpFile
+  IO.println <| baseLines == readLines
+  IO.FS.removeFile tmpFile
+
+/-- info: true -/
+#guard_msgs in
+#eval test