feat: move remote desktop (RDP/VNC/Telnet) into a first-party plugin

Relocates guacamole backend/frontend source and tests into
plugins/remote-desktop, following the ssh-terminal/docker pattern.

plugins/remote-desktop/frontend/guacamole-pointer.ts

@@ -0,0 +1,65 @@
+import Guacamole from "guacamole-common-js";
+import {
+  createScrollCoalescer,
+  isScrollButtonState,
+} from "./guacamole-scroll.js";
+
+export type GuacamoleTouchMode = "touchscreen" | "touchpad";
+
+/**
+ * Guacamole.Mouse listens for mousedown/mousemove/mouseup; the Touchscreen and
+ * Touchpad emulators listen only for touch events. The two sets do not overlap,
+ * so binding one instead of the other leaves that input dead.
+ *
+ * A touch-capable device is not a device without a pointer: laptops with a
+ * touchscreen report maxTouchPoints > 0 and are still driven by a mouse. The
+ * physical pointer is therefore always bound, and a touch emulator is layered
+ * on top when one is selected.
+ */
+export function bindPointerInput(
+  element: HTMLElement,
+  touchMode: GuacamoleTouchMode | null | undefined,
+  onState: (state: Guacamole.Mouse.State) => void,
+): () => void {
+  const coalescer = createScrollCoalescer((state) => {
+    onState(state as Guacamole.Mouse.State);
+  });
+  let expectingScrollRelease = false;
+
+  const handleState = (state: Guacamole.Mouse.State) => {
+    coalescer.notePointer(state);
+    if (isScrollButtonState(state)) {
+      coalescer.ingestClick(state.down ? 1 : -1);
+      expectingScrollRelease = true;
+      return;
+    }
+    if (
+      expectingScrollRelease &&
+      !state.left &&
+      !state.middle &&
+      !state.right
+    ) {
+      expectingScrollRelease = false;
+      return;
+    }
+    expectingScrollRelease = false;
+    onState(state);
+  };
+
+  const mouse = new Guacamole.Mouse(element);
+  mouse.onmousedown = mouse.onmouseup = mouse.onmousemove = handleState;
+
+  if (touchMode === "touchscreen") {
+    const touchscreen = new Guacamole.Mouse.Touchscreen(element);
+    touchscreen.onEach(["mousedown", "mousemove", "mouseup"], (event) =>
+      handleState(event.state),
+    );
+  } else if (touchMode === "touchpad") {
+    const touchpad = new Guacamole.Mouse.Touchpad(element);
+    touchpad.onEach(["mousedown", "mousemove", "mouseup"], (event) =>
+      handleState(event.state),
+    );
+  }
+
+  return () => coalescer.dispose();
+}