patch 9.1.1834: MS-Windows: not possible to highlight the title bar

patch 9.1.1834: MS-Windows: not possible to highlight the title bar

Problem:  MS-Windows: not possible to highlight the title bar
Solution: Make the title/caption bar configurable by introducing the
          'go-C' option value which allows to highlight it using the
          TitleBar and TitleBarNC highlighting groups (Mao-Yining).

Introduce titlebar color customization for Windows 11 GUI through
highlight groups and new 'guioptions' flag:

- Add 'C' flag to enable titlebar color customization (opt-in)
- New highlight groups: TitleBar (active) and TitleBarNC (inactive)
- Uses DWMWA_CAPTION_COLOR and DWMWA_TEXT_COLOR DWM attributes
- Dynamically loads dwmapi.dll for Windows 11 compatibility
- Defaults to system colors when set to NONE or feature disabled

closes: #18449

Signed-off-by: Mao-Yining <mao.yining@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>