Proxy: Add TUN inbound for Windows & Linux, including Android (#5464)

* Proxy: Implement tun raw network interface inbound support for Linux

* Proxy: Tun. Include "android" as build condition for build of tun_default implementation

* Proxy: Tun. Add .Close() cleanup calls to Handler.Init() where needed

* Proxy: Add Tun for Android

* Proxy: Tun. Implement Windows support

---------

Co-authored-by: yuhan6665 <1588741+yuhan6665@users.noreply.github.com>

proxy/tun/tun_default.go

@@ -0,0 +1,34 @@
+//go:build !linux && !windows && !android
+
+package tun
+
+import (
+	"github.com/xtls/xray-core/common/errors"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+)
+
+type DefaultTun struct {
+}
+
+// DefaultTun implements Tun
+var _ Tun = (*DefaultTun)(nil)
+
+// DefaultTun implements GVisorTun
+var _ GVisorTun = (*DefaultTun)(nil)
+
+// NewTun builds new tun interface handler
+func NewTun(options TunOptions) (Tun, error) {
+	return nil, errors.New("Tun is not supported on your platform")
+}
+
+func (t *DefaultTun) Start() error {
+	return errors.New("Tun is not supported on your platform")
+}
+
+func (t *DefaultTun) Close() error {
+	return errors.New("Tun is not supported on your platform")
+}
+
+func (t *DefaultTun) newEndpoint() (stack.LinkEndpoint, error) {
+	return nil, errors.New("Tun is not supported on your platform")
+}