Implement river-input-management-v1 and river-libinput-config-v1

Right now, the support is still incomplete (no way to set config) but
we get the devices and set them up and handle current/support events
for the river_libinput_device_v1 devices.

src/InputDevice.zig

@@ -0,0 +1,76 @@
+// SPDX-FileCopyrightText: 2026 Ben Buhse <me@benbuhse.email>
+//
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+const InputDevice = @This();
+
+river_input_device_v1: *river.InputDeviceV1,
+
+/// The LibinputDevice that corresponds to this same InputDevice.
+/// This comes later (and from a separate river protocol) and
+/// not all InputDevices are necessarily LibinputDevices, too,
+/// so it's optional.
+libinput_device: ?*LibinputDevice = null,
+
+type: ?Type = null,
+name: ?[]const u8 = null,
+
+link: wl.list.Link,
+
+pub fn create(river_input_device_v1: *river.InputDeviceV1) !*InputDevice {
+    const input_device = try utils.allocator.create(InputDevice);
+    errdefer input_device.destroy();
+
+    input_device.* = .{
+        .river_input_device_v1 = river_input_device_v1,
+        .link = undefined, // handled by the wl.List
+    };
+
+    input_device.river_input_device_v1.setListener(
+        *InputDevice,
+        riverInputDeviceV1Listener,
+        input_device,
+    );
+
+    return input_device;
+}
+
+pub fn destroy(input_device: *InputDevice) void {
+    input_device.link.remove();
+    utils.allocator.destroy(input_device);
+}
+
+fn riverInputDeviceV1Listener(river_input_device_v1: *river.InputDeviceV1, event: river.InputDeviceV1.Event, input_device: *InputDevice) void {
+    assert(input_device.river_input_device_v1 == river_input_device_v1);
+    switch (event) {
+        .removed => {
+            river_input_device_v1.destroy();
+            input_device.destroy();
+        },
+        .type => |ev| {
+            // This event is only sent once when the object is created
+            assert(input_device.type == null);
+            input_device.type = ev.type;
+        },
+        .name => |ev| {
+            // This event is only sent once when the object is created
+            assert(input_device.name == null);
+            input_device.name = mem.span(ev.name);
+        },
+    }
+}
+
+const std = @import("std");
+const assert = std.debug.assert;
+const mem = std.mem;
+
+const wayland = @import("wayland");
+const wl = wayland.client.wl;
+const river = wayland.client.river;
+const Type = river.InputDeviceV1.Type;
+
+const utils = @import("utils.zig");
+const Context = @import("Context.zig");
+const LibinputDevice = @import("LibinputDevice.zig");
+
+const log = std.log.scoped(.InputDevice);