Function snap_to_soft_tab_line_col 

pub fn snap_to_soft_tab_line_col(
    text: &Rope,
    line: usize,
    col: usize,
    direction: SnapDirection,
    tab_width: usize,
) -> usize

If the cursor is inside a soft tab at the start of the line, snap it to the nearest, left or right edge. This version takes a line/column and returns a column.