bug#53001: 29.0.50; xwidget-webkit: no mouseover text on pgtk

[akira]

In GNU Emacs 29.0.50 (build 1, aarch64-unknown-linux-gnu, GTK+ Version 3.24.30, 
cairo version 1.16.0)
Repository revision: ab5ee3e29e916d4009b301841e9780aad564a6a0
Repository branch: master
System Description: NixOS 22.05 (Quokka)

Configured using:
 'configure
 --prefix=/nix/store/0fiqa453abl4c1c28g0baqs9s274s7ff-emacs-pgtkgcc-20220103.0
 --disable-build-details --with-modules --with-x-toolkit=gtk3
 --with-cairo --with-xwidgets --with-native-compilation --with-pgtk'

Window manager: sway

Steps to reproduce:

- emacs -Q
- M-x xwidget-webkit-browse-url RET https://xkcd.com
- Hover mouse over the comic, there should be mousover text present

I also tested this on debian 11 under GNOME and observe the same
behavior. While emacs configured with the default with x+gtk3 the
mousover text works.

I also noticed that the cursor over "non-clickable" and non-text
elements is the I-beam cursor bar that is typically reserved for
hovering over select-able text elements. I would expect the cursor to be
the default mouse when hovering over, say, an image.