This commit adds the `border-native` resulting in the following:
```
--tmux[=[center|top|bottom|left|right][,SIZE[%]][,SIZE[%]][,border-native]]
```
By default, when not specified, the `-B` flag is passed to the
`tmux popup-window` command such that no border is drawn around
the tmux popup window.
When the `border-native` option is present, the `-B` flag is omitted
and the popup window is drawn using the border style configured in
the tmux config file.
Fixes#4156
Signed-off-by: Andreas Auernhammer <github@aead.dev>
Co-authored-by: Junegunn Choi <junegunn.c@gmail.com>