Add ability to get a list of the current page of buffers in the `buflist`

[mehalter]

It would be nice to have a way to query the heirline tabline with a buflist which buffers are currently displayed in the tabline during the pagination. This could be useful for setting up bindings to quickly select a buffer that is visible say I want to have a binding to select the 1st buffer or 2nd buffer but out of the visible list rather than the entire list itself. Note the word "visible" used here is for lack of a better word and is not the same as "is_visible" which is used for if a buffer is currently visible in a window of the editor.

There is currently documentation for setting up a buffer picker which is a great alternative, but it would be nice to be able to also get information on the list of visible buffers in the pagination. I looked through the source code and it looks like the buffer pages are internally managed and don't have a public access point. I'm not sure what the best approach for doing this efficiently, but just an idea!

Thanks so much for this amazing project!

[rebelot]

I guess that making internal pages and active_page buflist attributes would probably do. Then you can query self.pages[self.active_page] components to see what buffers they're pointing to

[mehalter]

That would be awesome!