Add support for TabbedPane foreground color on hover

[rkeen-siemens]

TabbedPane currently only has the ability to set the hover background (via "TabbedPane.hoverColor"). It would be nice to have the option to also set the background, perhaps via "TabbledPane.hoverForeground".

[DevCharly]

Implemented in latest 3.1-SNAPSHOT: https://github.com/JFormDesigner/FlatLaf#snapshots

There are 2 new (optional) UI properties:

TabbedPane.hoverForeground
TabbedPane.focusForeground

This allows e.g. following style:

• normal text color for selected tab
• dimmed text for non-selected tabs
• normal text color if mouse is over tab
• special text color for focused tab
• no tab background for hover and focused tab

TabbedPane.foreground = tint(@foreground,50%)
TabbedPane.selectedForeground = @foreground
TabbedPane.hoverForeground = @foreground
TabbedPane.focusForeground = @accentLinkColor
TabbedPane.hoverColor = null
TabbedPane.focusColor = null