vim-patch:9.0.2032: cannot get mouse click pos for tab or virt text (#25653)

Problem:  Cannot accurately get mouse clicking position when clicking on
          a TAB or with virtual text.
Solution: Add a "coladd" field to getmousepos() result.

closes: vim/vim#13335

f5a94d5165

runtime/lua/vim/_meta/vimfn.lua

@@ -3242,6 +3242,8 @@ function vim.fn.getmatches(win) end
 ---   wincol    column inside "winid"
 ---   line    text line inside "winid"
 ---   column    text column inside "winid"
+---   coladd    offset (in screen columns) from the
+---       start of the clicked char
 --- All numbers are 1-based.
 ---
 --- If not over a window, e.g. when in the command line, then only