Port `project_settings_changed` signal changes from `3.x` to `master`

[Calinou]

Godot version

4.0.alpha (1847094)

System information

Fedora 36, GeForce GTX 1080 (NVIDIA 510.68.02)

Issue description

#53296 has made it possible to use the project_settings_changed outside of editor builds, but this feature isn't available yet in master.

This issue is a reminder to port relevant functionality to avoid functional regressions for people upgrading from Godot 3.x to Godot 4.0.

Steps to reproduce

Try to find a project_settings_changed signal exposed to the scripting API in master.

Minimal reproduction project

N/A