[FEATURE] Support Automatic Adaption to Windows Accent Colors

[wolframhaussig]

Is your feature request related to a problem? Please describe.
Currently, we support automatically styling the application based on dark mode and high contast settings but we do NOT support the accent colors set in the windows settings.

Describe the solution you'd like
We should provide variables (e.g. VAR_WIN_ACCENT_COLOR) that can be used as a value instead of the actual color code in file themes and provide direct access to the color (e.g. via a property WindowsAccentColor) in the coded theme definitions.
The settings can be accessed in the registry key Computer\HKEY_CURRENT_USER\Software\Microsoft\Windows\DWM