Upgrade tao to gtk4-rs

[tweidinger]

We need to upgrade from gtk to gtk4-rs to migrate a unsoundness issue found in glib < 0.2.
Please claim this issue if you want to support or work on this and keep in mind this is a prioritized issue and we try to migrate as soon as possible. If the issue is already assigned to someone you can either reach out with comments or questions reach out for collaboration to the assigned person.

This transition includes:

• Upgrading gtk to gtk4-rs and handling all errors caused by the dependency change
• Handle all changes in a backwards compatible way if possible
  • Raise awareness to the working group if breaking changes are required
• Document migration errors that may be issues in the future or which were complicated to handle
• Reach out to the working group (alternatively @tweidinger first) if blockers or upstream issues are hit

[Captainpast]

Previously requests in #134 and #907

[conradhale]

I would like to help with this. I took a swing at this recently and the main blocker I ran into was related to the removal of X11-specific APIs in GTK4. Most of the removed APIs are related to window positioning. Continuing to support this in tauri seems like it would be tricky, and I personally think its fine to just remove these APIs since X11 isn't that popular anymore.

Some other notable changes:

• Removal of the widget 'draw' signal, we could support it again through a subclass of GtkWindow
• Removal of widget event signals, although most of them have replacements
• GtkContainer API is gone which is used by wry, but we could mimic it with a trait
• GdkWindow is now called GdkSurface
• Newer webkitgtk crates that should be able to replace the tauri ones
• Removal of the glib::Sender api from gtk-rs-core

I can try to get my in-progress code on github this weekend, but in the meantime please share any thoughts/opinions on supporting X11-specific features.

[conradhale]

Also webkitgtk recently got support for rendering with skia. As far as I'm aware this wasn't backported to the gtk3 version, so bumping to gtk4 should bring a noticeable performance improvement