active sheet gets pushed off crowded statusbar

[midichef]

Small description
The statusbar cannot keep the active sheet visible in the left statusbar when there are many sheets, as @aszenz helpfully pointed out in #2921.

Steps to reproduce
Open any sheet, then press A (open-new) repeatedly until the statusbar fills up with sheets. Once it's full, the name of the currently active sheet can no longer be seen.

The disp_lstatus_max option, recently improved for v3.4dev, does not solve this problem, because it always trims characters from the middle of the status bar. The active sheet stays visible only when it's one of the first or last sheets. When it is one of the middle sheets, it'll still be invisible.

[saulpw]

It's like we need a clipstr_nonmiddle or something that does the inverse of clipstr_middle, so that we can find the [:menu_active] markup in the sheetlist string and show the string around that, clipping the beginning and ending of the string if necessary.

[midichef]

What if we make BaseSheet.sheetlist truncate the full list of sheets, since the left status bar is the only place it's used?

It could build the sheet string outward from the active sheet, appending sheeets alternately to the left and to the right, until disp_lstatus_max is reached.

[aszenz]

Maybe the tabs can be horizontally scrollable just like regular columns

[saulpw]

@midichef I like that idea, it seems pretty straightforward and less code than my proposal. If you have the time and inclination, let's do it.

@aszenz that's certainly what people expect from spreadsheet tabs, but it would be a fair amount of code, and the interface would be clunky and/or depend on the mouse.