Problem: When `vim._extui` is enabled, the default tabline shows an
incorrect window count (e.g., "2" when only 1 window is visible). This
happens because the extui pager window has `focusable=true` (needed for
user interaction) but `hide=true` (not visible by default).
Solution: Modify the window counting logic in `statusline.c` and
`ex_docmd.c:ex_tabs()` to also exclude hidden windows
(`wp->w_config.hide`), not just non-focusable windows.
Also updates test expectations in `cmdline2_spec.lua` which previously
expected the incorrect window count "2" when extui was enabled. The test
now correctly expects no window count indicator when only 1 visible
window exists.
Fixes#36759
ad438b6b14