Scripts

Is there a way to get what object is on specific coordinates?

For example GetObjectFromLocation(x,y)

The developers haven't provided a direct way to do this.
As an alternative, you can create a table during map initialization where the key is the map coordinate and the value is the object's name.

Or is the only way to iterate through all existing objects on the map and check them one by one?

In general, there is no function that returns all objects on the map.
You can find some of them by a specific type, such as SKELETON, SAWMILL, HERO, etc. Additional manipulations are needed, for example, manually naming objects.
In principle, this is the problem, although it is feasible, but quite laborious.

Here is this extended editor. But if it doesn't allow you to add objects, then what is it for?

I provided examples.

it allows you to open game resources, select the necessary windows (?), pack changes into a map archive, maybe something else