Jump to last visible line and middle visible line are incorrect when code is folded

[forivall]

The commands dance.select.lastVisibleLine, dance.select.middleVisibleLine and their jump / extend variants dont work correctly when there is folded code. I think it's because when code is folded, then there are multiple visible ranges, and the first visible range is just the code on the screen until the beginning of the first fold.

Proposed fix: master...forivall:vscode-dance:patch-1