Use winpty to launch fzf in Git bash (mintty)

Close #3806

Known limitation:
* --height cannot be used

src/winpty_windows.go

@@ -0,0 +1,29 @@
+//go:build windows
+
+package fzf
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+)
+
+func runWinpty(args []string, opts *Options) (int, error) {
+	sh, err := sh()
+	if err != nil {
+		return ExitError, err
+	}
+
+	argStr := escapeSingleQuote(args[0])
+	for _, arg := range args[1:] {
+		argStr += " " + escapeSingleQuote(arg)
+	}
+	argStr += ` --no-winpty --no-height`
+
+	return runProxy(argStr, func(temp string) *exec.Cmd {
+		cmd := exec.Command(sh, "-c", fmt.Sprintf(`winpty < /dev/tty > /dev/tty -- sh %q`, temp))
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		return cmd
+	}, opts, false)
+}