Removal off "confirm" callback in favour of new method that shares
existing operator dialog code and allows python configuration.

@@ -213,0 +214,4 @@
+                                wmEvent * /*event*/,
+                                const char *title,
+                                const char *message,
+                                const char *message2,

@@ -213,0 +220,4 @@
+                                const int size,
+                                const int position,
+                                const bool cancel_default,
+                                const bool mouse_move_quit,

@@ -1717,1 +1545,3 @@
-  uiItemS_ex(layout, 0.3f);
+  /* Break Message into multiple lines. */
+  std::vector<std::string> message_lines;
+  std::istringstream origStream(data->message);

@@ -1718,0 +1547,4 @@
+  std::istringstream origStream(data->message);
+  std::string line;
+  while (std::getline(origStream, line)) {
+    if (!line.empty()) {

@@ -1718,0 +1558,4 @@
+  dialog_width += (data->icon == ALERT_ICON_NONE) ? 0 : icon_size;
+
+  /* Adjust width if the button text is long. */
+  int longest_button_text = std::max(

@@ -1718,0 +1560,4 @@
+  /* Adjust width if the button text is long. */
+  int longest_button_text = std::max(
+      BLF_width(style->widget.uifont_id, data->confirm_text.c_str(), data->confirm_text.length()),
+      BLF_width(style->widget.uifont_id, IFACE_("Cancel"), BLF_DRAW_STR_DUMMY_MAX));

@@ -1718,0 +1561,4 @@
+  int longest_button_text = std::max(
+      BLF_width(style->widget.uifont_id, data->confirm_text.c_str(), data->confirm_text.length()),
+      BLF_width(style->widget.uifont_id, IFACE_("Cancel"), BLF_DRAW_STR_DUMMY_MAX));
+  dialog_width = std::max(dialog_width, 3 * longest_button_text);

@@ -1804,1 +1665,3 @@
-    UI_block_bounds_set_popup(block, 10 * UI_SCALE_FAC, bounds_offset);
+    bounds_offset[0] = uiLayoutGetWidth(layout) * (windows_layout ? -0.33f : -0.66f);
+    bounds_offset[1] = int(UI_UNIT_Y * (small ? 1.8 : 3.1));
+    UI_block_bounds_set_popup(block, padding, bounds_offset);

@@ -1718,0 +1548,4 @@
+  std::string line;
+  while (std::getline(origStream, line)) {
+    if (!line.empty()) {
+      message_lines.push_back(line);

@@ -1367,4 +1216,0 @@
-
-  UI_block_func_set(block, nullptr, nullptr, nullptr);
-  UI_but_func_set(confirm_but, wm_operator_block_confirm, op, block);
-  UI_but_func_set(cancel_but, wm_operator_block_cancel, op, block);

@@ -1805,0 +1656,4 @@
+    const float button_center_x = windows_layout ? -0.33f : -0.66f;
+    const float button_center_y = small ? 1.9f : 3.1f;
+    const int bounds_offset[2] = {button_center_x * uiLayoutGetWidth(layout),
+                                  button_center_y * UI_UNIT_X};