PipeWire video capture: set device unique ID during initialization

This is what Firefox implementation relies on and I can see that also
the V4L2 implementation is doing the same.

Bug: webrtc:15087
Change-Id: I641062ba879b6ef83e31af79ecc9d06fdae54adb
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/301320
Commit-Queue: Jan Grulich <grulja@gmail.com>
Reviewed-by: Alexander Cooper <alcooper@chromium.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39869}

modules/video_capture/linux/video_capture_pipewire.cc

@@ -62,6 +62,10 @@ int32_t VideoCaptureModulePipeWire::Init(const char* deviceUniqueId) {
 
   node_id_ = id.value();
 
+  const int len = strlen(deviceUniqueId);
+  _deviceUniqueId = new (std::nothrow) char[len + 1];
+  memcpy(_deviceUniqueId, deviceUniqueId, len + 1);
+
   return 0;
 }