VPN-6783: detect system theme changes

[mcleinman]

Description

Detect when the system theme changes. VPN-6178 will add the code that actually exposes this to the user.

This will not work on Qt version <6.5, to keep it in line with the prior system color work.

Reference

VPN-6783

Checklist

• My code follows the style guidelines for this project
• I have not added any packages that contain high risk or unknown licenses (GPL, LGPL, MPL, etc. consult with DevOps if in question)
• I have performed a self review of my own code
• I have commented my code PARTICULARLY in hard to understand areas
• I have added thorough tests where needed

[strseb]

I would prefer not to merge an empty connect - as i doubt the compiler will optimize that away :)
maybe we can keep this open until we start VPN-6178?

[mcleinman]

I would prefer not to merge an empty connect - as i doubt the compiler will optimize that away :) maybe we can keep this open until we start VPN-6178?

What if we keep this code in there, but fully comment it out for now?