Main: Use ImageLoader directly instead of Image::load

Image::load is now issuing warnings (since ef50957) to prevent users
from using it to load images at runtime which would be included in
their exported game.

So we now use ImageLoader explicitly instead for the custom-handled
cases in Main.

Fixes #21072, supersedes #22321.

main/main.cpp

@@ -34,6 +34,7 @@
 #include "core/io/file_access_network.h"
 #include "core/io/file_access_pack.h"
 #include "core/io/file_access_zip.h"
+#include "core/io/image_loader.h"
 #include "core/io/ip.h"
 #include "core/io/resource_loader.h"
 #include "core/io/stream_peer_ssl.h"
@@ -1124,9 +1125,8 @@ Error Main::setup2(Thread::ID p_main_tid_override) {
 		boot_logo_path = boot_logo_path.strip_edges();
 
 		if (boot_logo_path != String()) {
-			print_line("Boot splash path: " + boot_logo_path);
 			boot_logo.instance();
-			Error err = boot_logo->load(boot_logo_path);
+			Error err = ImageLoader::load_image(boot_logo_path, boot_logo);
 			if (err)
 				ERR_PRINTS("Non-existing or invalid boot splash at: " + boot_logo_path + ". Loading default splash.");
 		}
@@ -1707,7 +1707,7 @@ bool Main::start() {
 				if (iconpath != "") {
 					Ref<Image> icon;
 					icon.instance();
-					if (icon->load(iconpath) == OK) {
+					if (ImageLoader::load_image(iconpath, icon) == OK) {
 						OS::get_singleton()->set_icon(icon);
 						hasicon = true;
 					}