[TextEdit] Use style margins for selection in read-only mode.

[bruvzg]

Fixes #92312

Adds margins in the same way draw code do:

godot/scene/gui/text_edit.cpp

Lines 973 to 979 in 1e6b11d

	if (!editable) {
	ofs_x = theme_cache.style_readonly->get_offset().x / 2;
	ofs_x -= theme_cache.style_normal->get_offset().x / 2;
	ofs_y = theme_cache.style_readonly->get_offset().y / 2;
	} else {
	ofs_y = theme_cache.style_normal->get_offset().y / 2;
	}

[akien-mga]

The unit test for TextEdit seems to be failing.

[bruvzg]

The unit test for TextEdit seems to be failing.

Should be fixed, but seems like draw code use strange values as well, this is not directly related to the specific issue, but it might have a lot more issues if different margins are set for different styles. I'll check it later.

[timothyqiu]

I'm a bit curious why the offset (vector of the left margin and top margin) was divided by 2. 🤔

[bruvzg]

I'm a bit curious why the offset (vector of the left margin and top margin) was divided by 2. 🤔

No idea, but it is used like this when drawing.

[akien-mga]

Thanks!