Refactor runtime code for code sharing

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

pkg/stdio/platform.go

@@ -0,0 +1,33 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package stdio
+
+import (
+	"context"
+	"sync"
+
+	"github.com/containerd/console"
+)
+
+// Platform handles platform-specific behavior that may differs across
+// platform implementations
+type Platform interface {
+	CopyConsole(ctx context.Context, console console.Console, stdin, stdout, stderr string,
+		wg *sync.WaitGroup) (console.Console, error)
+	ShutdownConsole(ctx context.Context, console console.Console) error
+	Close() error
+}