Copy&Paste does not work on VNC
Description of problem:
Cannot copy&paste between host and guest when vnc is used (gtk works fine).
Steps to reproduce:
1. Build qemu 6.2-rc2 using the following `./configure` options:
```
--prefix=$HOME/.bin --target-list=x86_64-softmmu --enable-kvm --enable-vnc --enable-gtk --enable-vte --enable-xkbcommon --enable-sdl --enable-spice --enable-spice-protocol --enable-virglrenderer --enable-opengl --enable-guest-agent --enable-avx2 --enable-hax --enable-system --enable-linux-user --enable-libssh --enable-linux-aio --enable-linux-io-uring --enable-modules --enable-fuse --enable-fuse-lseek
```
2. Run the above qemu command using vnc server. Connect to the VM desktop using `vncviewer :5900` where vncviewer is downloaded from [here](https://www.realvnc.com/en/connect/download/viewer/).
3. Try to copy and paste something in the terminal between host and guest. It doesn't work.
Additional information:
I'm following [this article](https://www.kraxel.org/blog/2021/05/qemu-cut-paste/) which says copy&paste is supported on vnc.