feat(windows): Customizable title bar style

[bryphe]

Issue: There are several quirks on Windows with the 'undecorated' Windows style - issues like:

• Windows: Keyboard shortcuts for window movement is broken ( Win + Right / Left Arrow) #3730
• Window has no shadow on Windows #3071
• Part of onvim in fullscreen is visible on a second monitor #3063

Fix: These can be deal-breakers for use as a daily editor, so until we have those fixed for the 'undecorated' Windows, change the default setting to use the native titlebar.

This introduces a new setting - window.titleBarStyle that can be "native" or "custom". The "custom" titlebar looks nicer, because it is themed and custom rendered, however it has the above quirks. On Windows, change the default to "native".

In addition, this pushes up the configuration loading sooner in the startup cycle, so we can pick up configuration settings like "window.titleBarStyle" prior to opening the window.

Todo:

• Fix margin on Windows, based on whether we are using the decorated window or not
• Test OSX
• Test Windows (both settings)
• Test on Linux (both settings)