tabline: All of the duplicated buffers are highlighted in buffers list

[KSR-Yasuda]

environment

• vim: VIM - Vi IMproved 8.2 (2019 Dec 12, compiled Nov 22 2021 19:31:05) patch 1-3582
• vim-airline: 9049793
• OS: Windows 10 Pro 12H2 (Version 10.0.19044.1586)
  • Git-for-Windows version 2.35.1.windows.2.7.g158a30d60b.20220224121117
• Have you reproduced with a minimal vimrc: yes
• What is your airline configuration:
  • let g:airline#extensions#tabline#enabled = 1

if you are using terminal:

• terminal: Git Bash (Git-for-Windows)
• $TERM variable: xterm-256color
• color configuration (:set t_Co?): 256

if you are using Neovim: No

• does it happen in Vim: Yes

actual behavior

" Open new buffers `a`, `b`
:enew
:f a

:new
:f b

" Load the buffer `a`, duplicately
:new
:b a

" Create a tab to show `buffers` list in tabline
:tabnew

" Go back to the first tab
:1 tabn

Tabline extension shows buffers list in the tab.

If the same buffers are opened duplicately, the buffers are listed duplicately
(i.e. Buffers a, b, and the same a are listed).

Also, if one of the window of the buffer is active, all labels of the buffer are highlighted
(i.e. If either one of a window is focused, both two a are highlighted).

expected behavior

If it means buffer list, duplicated buffers should be stripped.
Or it means window list, it should highlight only the label corresponding to the active window.

Showing as window list is more useful, though, it may be more complex to fix.

The buffer list is not refreshed on some of window managing hotkeys
(e.g. Ctrl-s, Ctrl-v for horisontal / vertical split;
Ctrl-c for window close, if it moves to the same (duplicated buffer) of the closing one).

So, the current implementation is rather close to buffer list.