refactor: add selection_pos_to_width and get_replace_selection functions

src/tui/editor.zig

@@ -5602,6 +5602,11 @@ pub const Editor = struct {
         }
     }
 
+    pub fn selection_pos_to_width(self: *Self, sel_: Selection) ?Selection {
+        const root = self.buf_root() catch return null;
+        return sel_.from_pos(root, self.metrics) catch null;
+    }
+
     fn count_lines(content: []const u8) struct { usize, usize } {
         var pos = content;
         var offset = content.len;