@icon larger than 32x32 warning

Warn user of `@icon` sizes larger than 32x32. This resolution is good
for hiDPI displays; higher resolutions effect performance.
Make mention of this in the docs as well.

editor/editor_node.cpp

@@ -4144,6 +4144,9 @@ Ref<ImageTexture> EditorNode::_load_custom_class_icon(const String &p_path) cons
 		Ref<Image> img = memnew(Image);
 		Error err = ImageLoader::load_image(p_path, img);
 		if (err == OK) {
+			if (img->get_size() > Size2(32, 32)) {
+				WARN_PRINT_ONCE("The class icon '" + p_path + "' is larger than the recommended size of 32x32. This can cause performance issues.");
+			}
 			img->resize(16 * EDSCALE, 16 * EDSCALE, Image::INTERPOLATE_LANCZOS);
 			return ImageTexture::create_from_image(img);
 		}

modules/gdscript/doc_classes/@GDScript.xml

@@ -551,7 +551,7 @@
 				[codeblock]
 				@icon("res://path/to/class/icon.svg")
 				[/codeblock]
-				[b]Note:[/b] Only the script can have a custom icon. Inner classes are not supported.
+				[b]Note:[/b] Only the script can have a custom icon. Inner classes are not supported. The recommended icon size is 32x32, as this resolution looks good on hiDPI displays (but higher resolutions can cause performance issues).
 			</description>
 		</annotation>
 		<annotation name="@onready">