fix: Run expect tests on Windows with conpty pseudo-terminal (#276)

This brings together a bunch of random, partially implemented packages for support of the new(ish) Windows [`conpty`](https://devblogs.microsoft.com/commandline/windows-command-line-introducing-the-windows-pseudo-console-conpty/) API - such that we can leverage the `expect` style of CLI tests, but in a way that works in Linux/OSX `pty`s and Windows `conpty`.

These include:
- Vendoring the `go-expect` library from Netflix w/ some tweaks to work cross-platform
- Vendoring the `pty` cross-platform implementation from [waypoint-plugin-sdk](b55c787a65/internal/pkg/pty)
- Vendoring the `conpty` Windows-specific implementation from [waypoint-plugin-sdk](b55c787a65/internal/pkg/conpty)
- Adjusting the `pty` interface to work with `go-expect` + the cross-plat version

There were several limitations with the current packages:
- `go-expect` requires the same `os.File` (TTY) for input / output, but `conhost` requires separate file handles
- `conpty` does not handle input, only output
- The cross-platform `pty` didn't expose the full set of primitives needed for `console`

Therefore, the following changes were made:
- Handling of `stdin` was added to the `conpty` interface
- We weren't using the full extent of the `go-expect` interface, so some portions were removed (ie, exec'ing a process) to simplify our implementation and make it easier to extend cross-platform
- Instead of `console` exposing just a `Tty`, it exposes an `InTty` and `OutTty`, to help encapsulate the difference on Windows (on Linux, these point to the same pipe)

Future improvements:
- The `isatty` implementation doesn't support accurate detection of `conhost` pty's without an associated process. In lieu of a more robust check, I've added a `--force-tty` flag intended for test case use - that forces the CLI to run in tty mode.
- It seems the windows implementation doesn't support setting a deadline. This is needed for the expect.Timeout API, but isn't used by us yet.

Fixes #241

expect/test_console.go

@@ -0,0 +1,45 @@
+package expect
+
+import (
+	"bufio"
+	"io"
+	"regexp"
+	"testing"
+
+	"github.com/spf13/cobra"
+	"github.com/stretchr/testify/require"
+)
+
+var (
+	// Used to ensure terminal output doesn't have anything crazy!
+	// See: https://stackoverflow.com/a/29497680
+	stripAnsi = regexp.MustCompile("[\u001B\u009B][[\\]()#;?]*(?:(?:(?:[a-zA-Z\\d]*(?:;[a-zA-Z\\d]*)*)?\u0007)|(?:(?:\\d{1,4}(?:;\\d{0,4})*)?[\\dA-PRZcf-ntqry=><~]))")
+)
+
+// NewTestConsole creates a new TTY bound to the command provided.
+// All ANSI escape codes are stripped to provide clean output.
+func NewTestConsole(t *testing.T, cmd *cobra.Command) *Console {
+	reader, writer := io.Pipe()
+	scanner := bufio.NewScanner(reader)
+	t.Cleanup(func() {
+		_ = reader.Close()
+		_ = writer.Close()
+	})
+	go func() {
+		for scanner.Scan() {
+			if scanner.Err() != nil {
+				return
+			}
+			t.Log(stripAnsi.ReplaceAllString(scanner.Text(), ""))
+		}
+	}()
+
+	console, err := NewConsole(WithStdout(writer))
+	require.NoError(t, err)
+	t.Cleanup(func() {
+		console.Close()
+	})
+	cmd.SetIn(console.InTty())
+	cmd.SetOut(console.OutTty())
+	return console
+}