Modernize borders and tab controls in the Windows LAF

The tab components used for TopComponents and the Project/Navigator sidebar look somewhat dated on the Windows LAF, and need improvements for HiDPI screens. I'll be making improvements on this for my NetBeans Platform-based application, and will likely be making an upstream PR for this in the future (which will benefit the IDE and other NetBeans Platform apps).

Specific improvements planned:

• Make the sidebar and TopComponent tabs consistent, and modernize the look of the tabs a bit.
• Remove out-of-fashion gradients.
• Remove out-of-fashion bevels.
• Get rid of the extra borders in the sidebar (Projects/Files/Services in the IDE).
• Make line thicknesses HiDPI-safe.
• Make lines line up and connect on HiDPI scalings above 100%.

HiDPI icons for the Windows LAF tab controls were previously added in NETBEANS-1238.  Improvements to borders on HiDPI screens were done in NETBEANS-2646. Various other HiDPI fixes in the Windows LAF were done in NETBEANS-3592.