dots-v2: hide cursor during output

Contributes to gotestyourself#352

Currently, as the new screen is written the cursor jumps around the
terminal. This hides it, writes everything else, then returns it.

Prior art:
https://github.com/docker/compose/blob/80856eacafcf96d6f27e74c07e42386fe662f8ef/pkg/progress/tty.go#L160-L162

internal/dotwriter/writer.go

@@ -30,6 +30,7 @@ func (w *Writer) Flush() error {
 	if w.buf.Len() == 0 {
 		return nil
 	}
+	defer w.hideCursor()()
 	w.clearLines(w.lineCount)
 	w.lineCount = bytes.Count(w.buf.Bytes(), []byte{'\n'})
 	_, err := w.out.Write(w.buf.Bytes())

internal/dotwriter/writer_posix.go

@@ -10,7 +10,17 @@ import (
 
 // clear the line and move the cursor up
 var clear = fmt.Sprintf("%c[%dA%c[2K", ESC, 1, ESC)
+var hide = fmt.Sprintf("%c[?25l", ESC)
+var show = fmt.Sprintf("%c[?25h", ESC)
 
 func (w *Writer) clearLines(count int) {
 	_, _ = fmt.Fprint(w.out, strings.Repeat(clear, count))
 }
+
+// hideCursor hides the cursor and returns a function to restore the cursor back.
+func (w *Writer) hideCursor() func() {
+	_, _ = fmt.Fprint(w.out, hide)
+	return func() {
+		_, _ = fmt.Fprint(w.out, show)
+	}
+}

internal/dotwriter/writer_windows.go

@@ -1,3 +1,4 @@
+//go:build windows
 // +build windows
 
 package dotwriter
@@ -70,3 +71,8 @@ func isConsole(fd uintptr) bool {
 	err := windows.GetConsoleMode(windows.Handle(fd), &mode)
 	return err == nil
 }
+
+// This may work on Windows but I am not sure how to do it and its optional. For now, just do nothing.
+func (w *Writer) hideCursor() func() {
+	return func() {}
+}