patch 9.2.0360: Cannot handle mouse-clicks in the tabpanel

patch 9.2.0360: Cannot handle mouse-clicks in the tabpanel

Problem:  Cannot handle mouse-clicks in the tabpanel
Solution: Add support using the %[FuncName] atom for the tabpanel
          (Yasuhiro Matsumoto)

Extend the statusline/tabline click region mechanism to work with
'tabpanel'. The callback receives a dict with "area" set to "tabpanel"
and a "tabnr" key indicating which tab page label was clicked.

closes: #19960

Signed-off-by: Yasuhiro Matsumoto <mattn.jp@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>