[serial_proxy] Add USB_SERIAL port type and device identity (#19308)

Co-authored-by: J. Nick Koston <nick@home-assistant.io>
Co-authored-by: J. Nick Koston <nick@koston.org>
Co-authored-by: Keith Burzinski <kbx81x@gmail.com>

tests/benchmarks/stubs/esphome/components/serial_proxy/serial_proxy.h

@@ -49,6 +49,7 @@ class SerialProxy {
   uint32_t get_modem_pins() const { return 0; }
   uint32_t get_configured_modem_pins() const { return 0; }
   SerialProxyResult flush_port(api::APIConnection *api_connection) { return SerialProxyResult::SERIAL_PROXY_RESULT_OK; }
+  void send_identity(api::APIConnection *api_connection) {}
 
  protected:
   uint32_t instance_index_{0};

tests/components/serial_proxy/test-usb.esp32-s3-idf.yaml

@@ -0,0 +1,30 @@
+# A hardware UART port alongside the USB one, so the USB identity define is exercised on a
+# port that has no USB channel
+packages:
+  uart: !include ../../test_build_components/common/uart/esp32-idf.yaml
+
+wifi:
+  ssid: MySSID
+  password: password1
+
+api:
+
+usb_host:
+
+usb_uart:
+  - type: CDC_ACM
+    vid: 0x303A
+    pid: 0x831A
+    channels:
+      - id: usb_serial_channel
+        baud_rate: 460800
+
+serial_proxy:
+  - id: serial_proxy_usb
+    uart_id: usb_serial_channel
+    name: USB Serial Port
+    port_type: USB_SERIAL
+  - id: serial_proxy_hw
+    uart_id: uart_bus
+    name: Hardware Serial Port
+    port_type: TTL