TabView - expose tab border color and tab selected color

[AlastairOZ]

I have a suggestion for the TabView

It would be nice if you could expose the tab border color and tab selected color

In _tab class:

        decoration: BoxDecoration(
          borderRadius: borderRadius,

          // if selected, the background is painted by _TabPainter
          color: widget.selected ? null : backgroundColor,
        ),

Suggested change:

        decoration: BoxDecoration(
          borderRadius: borderRadius,
          border: Border(
            top: BorderSide(color: widget.tabBorderColor ?? Colors.transparent),
            left: BorderSide(color: widget.tabBorderColor ?? Colors.transparent),
            right: BorderSide(color: widget.tabBorderColor ?? Colors.transparent),
          ),
          // if selected, the background is painted by _TabPainter
          color: widget.selected ? widget.tabSelectedColor : backgroundColor,
        ),