snippets: add hci-uart-native-sim

Enable connecting native sim to a physical board running hci_uart
without usage of Bumble or other intermediary steps, but rather using
common h4 hardware driver.

Most commonly used port is USB CDC-ACM, as by default for most nRF
boards.

Signed-off-by: Dmitrii Sharshakov <d3dx12.xx@gmail.com>

snippets/hci-uart-native-sim/README.rst

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+.. _snippet-hci-uart-native-sim:
+
+Native Simulator support for hci_uart Snippet (hci-uart-native-sim)
+###################################################################
+
+.. code-block:: console
+
+   west build -S hci-uart-native-sim [...]
+
+Overview
+********
+
+This snippet allows to use hci_uart connected to the host computer
+with the Native Simulator. It is useful for testing with a real
+Bluetooth controller, such as a device running Zephyr.

snippets/hci-uart-native-sim/hci-uart-native-sim.conf

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+# zephyr,native-tty-uart has a high load order
+CONFIG_BT_HCI_INIT_PRIORITY=55
+
+CONFIG_BT_BUF_EVT_RX_SIZE=255
+CONFIG_BT_BUF_ACL_RX_SIZE=255
+CONFIG_BT_BUF_ACL_TX_SIZE=251
+CONFIG_BT_BUF_CMD_TX_SIZE=255
+CONFIG_BT_CTLR_SCAN_DATA_LEN_MAX=191

snippets/hci-uart-native-sim/hci-uart-native-sim.overlay

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+/*
+ * Copyright (c) 2025 Dmitrii Sharshakov
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&bt_hci_userchan {
+	status = "disabled";
+};
+
+/ {
+	chosen {
+		zephyr,bt-hci = &bt_hci_uart;
+	};
+
+	hci_uart: hci_uart {
+		compatible = "zephyr,native-tty-uart";
+		status = "okay";
+		current-speed = <2000000>;
+		serial-port = "/dev/ttyACM0";
+
+		bt_hci_uart: bt_hci_uart {
+			compatible = "zephyr,bt-hci-uart";
+			status = "okay";
+		};
+	};
+};

snippets/hci-uart-native-sim/snippet.yml

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+name: hci-uart-native-sim
+append:
+  EXTRA_CONF_FILE: hci-uart-native-sim.conf
+  EXTRA_DTC_OVERLAY_FILE: hci-uart-native-sim.overlay