[uart_mux] New component to share a UART between a CDC-ACM bridge and local consumers (#19066)

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>
Co-authored-by: J. Nick Koston <nick@koston.org>

tests/components/uart_mux/common.yaml

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+tinyusb:
+  id: tinyusb_test
+  on_mount:
+    - uart_mux.select_bridge: mux_0
+  on_unmount:
+    - uart_mux.select_local: mux_0
+  usb_manufacturer_str: ESPHomeTestManufacturer
+  usb_product_id: 0x1234
+  usb_product_str: ESPHomeTestProduct
+  usb_vendor_id: 0x2345
+
+uart:
+  - id: uart_0
+    tx_pin: 14
+    rx_pin: 13
+    baud_rate: 115200
+
+usb_cdc_acm:
+  interfaces:
+    - id: cdc_acm_1
+
+bridge:
+  - platform: cdc_acm_uart
+    id: bridge_0
+    uart_id: uart_0
+    usb_cdc_acm_id: cdc_acm_1
+
+uart_mux:
+  - id: mux_0
+    bridge_id: bridge_0
+    initial_route: local
+
+interval:
+  - interval: 60s
+    then:
+      - if:
+          condition:
+            uart_mux.is_local: mux_0
+          then:
+            - lambda: |-
+                uint8_t byte;
+                if (id(mux_0).available() && id(mux_0).read_byte(&byte)) {
+                  id(mux_0).write_byte(byte);
+                }

tests/components/uart_mux/test.esp32-p4-idf.yaml

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+packages:
+  uart_mux: !include common.yaml

tests/components/uart_mux/test.esp32-s2-idf.yaml

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+# ESP32-S2 has no USB_SERIAL_JTAG, so the logger defaults to USB_CDC, which shares
+# the USB OTG peripheral with tinyusb. Use a hardware UART for logging instead.
+logger:
+  hardware_uart: UART0
+
+packages:
+  uart_mux: !include common.yaml

tests/components/uart_mux/test.esp32-s3-idf.yaml

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+packages:
+  uart_mux: !include common.yaml