Platform-consistent placement of title pane contents

[kirill-grouchnikov]

Similar to the recent changes to option pane button order and alignment, add platform-specific defaults for alignment of title pane icon, title and buttons

• Mac - buttons on leading (left under LTR), title centered, icon next to title
• Windows - buttons on trailing (right under LTR), title on leading, icon next to title
• Gnome - buttons on trailing (right under LTR), title centered, no icon
• KDE - buttons on trailing (right under LTR), title centered, icon on leading

expose APIs on SubstanceCortex.GlobalScope to control custom alignment

[kirill-grouchnikov]

The newly added API on SubstanceCortex allows configuring the placement of title pane icon, text and buttons.

The default remains the Swing one - leading icon, text right next to it and buttons as trailing. I've tried switching to the platform order, but it looks really ugly on macOS with JMenuBar right below the decorated title pane. So the PLATFORM option is there for apps with UI structure that makes it play nicely with it, but it's not the new default.