feat: add whitespace_mode external

src/config.zig

@@ -114,6 +114,7 @@ pub const WhitespaceMode = enum {
     leading,
     eol,
     tabs,
+    external,
     visible,
     full,
     none,

src/tui/editor.zig

@@ -1562,6 +1562,18 @@ pub const Editor = struct {
                                 cell.cell.char.grapheme = c;
                         }
                     },
+                    .external => {
+                        if (leading) {
+                            if (get_whitespace_char(cell_type, next_cell_type)) |c|
+                                cell.cell.char.grapheme = c;
+                        }
+                        if (cell_type == .eol)
+                            cell.cell.char.grapheme = char.eol;
+                        if (cell_type == .tab or cell_type == .extension) {
+                            if (get_whitespace_char(cell_type, next_cell_type)) |c|
+                                cell.cell.char.grapheme = c;
+                        }
+                    },
                     .visible => {
                         if (get_whitespace_char(cell_type, next_cell_type)) |c|
                             cell.cell.char.grapheme = c;

src/tui/tui.zig

@@ -1002,7 +1002,8 @@ const cmds = struct {
             .indent => .leading,
             .leading => .eol,
             .eol => .tabs,
-            .tabs => .visible,
+            .tabs => .external,
+            .external => .visible,
             .visible => .full,
             .full => .none,
         };