Support "Auto" scaling on Windows

[capricorn8]

Frequent feedback from users is that the focus point window exceeds their screen size.
While the plugin offers a means to handle this problem, and this is also part of the installation steps - it doesn't come as a surprise that users do not read documentation.

To avoid more users asking the same question, a mechanism is introduced so that the plugin can use the same exact scaling level as set in Windows settings (System, Display, Scale).

A new entry "Auto" is introduced that triggers the plugin to fetch the dpi scaling value from Windows Registry (HKCU\Control Pane\Desktop, LogPixels) and use this value to reduce the size of both Focus Points Viewer and Metadata Viewer dialog windows.

The scaling factor is also logged:

03/01/2025 17:33:07 INFO FOCUSPOINTDIALOG | Display scaling level 115%

[capricorn8]

The registry key HKCU\Control Pane\Desktop, LogPixels only exists if a custom scale factor has been set (e.g. "115%).

In order to determine the current display scaling including predefined scaling factors (100%, 125%, 150% etc.) the key HKEY_CURRENT_USER\Control Panel\Desktop\WindowMetrics, AppliedDPI needs to be queried.