add gui.confirm(...)

doc/en/scripting/builtins/libgui.md

@@ -61,3 +61,21 @@ gui.escape_markup(
 ```
 
 Escapes markup in text.
+
+```lua
+gui.confirm(
+    -- message (does not translate automatically, use gui.str(...))
+    message: str,
+    -- function called upon confirmation
+    on_confirm: function() -> nil,
+    -- function called upon denial/cancellation
+    [optional] on_deny: function() -> nil,
+    -- text for the confirmation button (default: "Yes")
+    -- use an empty string for the default value if you want to specify no_text.
+    [optional] yes_text: str,
+    -- text for the denial button (default: "No")
+    [optional] no_text: str,
+)
+```
+
+Requests confirmation from the user for an action. **Does not** stop code execution.