On Windows platform when viewing system fonts folder, also show fonts
that are only installed for that user.

On Windows most fonts are found in C:\Windows\Fonts. However, viewing this folder from outside Blender shows more fonts than we see in Blender. This is because per-user fonts are stored elsewhere. The operating system is nice enough to automagically combine the System and User lists into one, but Blender only shows the fonts that are actually in the folder.

It used to be that you were given a choice when installing fonts, so you could install for yourself or "all users". If you don't have permissions it could be that "for yourself" is the only option. Then the font is installed in a hard-to-find location: C:\Users\(username)\AppData\Local\Microsoft\Windows\Fonts. With Windows 11 it seems that users are no longer asked, but instead all fonts are treated as per-user.

This patch makes Blender do the same thing as the OS: combining both folders into one. Therefore what you see in Blender matches what you see outside Blender.