[HTML5] Make home path persistent in editor.

We used to only persist specific sub-folder of /home/web_user/ when
running the Web Editor. This resulted in bad UX about default project
creation path etc.
This PR makes the whole folder persistent, move the zip preloading to a
different folder (to avoid persisting it), and automatically prompt the
user to import it if present.

misc/dist/html/editor.html

@@ -326,7 +326,7 @@
 
 		function startEditor(zip) {
 			const INDETERMINATE_STATUS_STEP_MS = 100;
-			const persistentPaths = ['/home/web_user/.config', '/home/web_user/.cache', '/home/web_user/projects'];
+			const persistentPaths = ['/home/web_user/'];
 
 			var editorCanvas = document.getElementById('editor-canvas');
 			var gameCanvas = document.getElementById('game-canvas');
@@ -493,11 +493,11 @@
 				engine.setUnloadAfterInit(false); // Don't want to reload when starting game.
 				engine.init('godot.tools').then(function() {
 					if (zip) {
-						engine.copyToFS("/home/web_user/preload.zip", zip);
+						engine.copyToFS("/tmp/preload.zip", zip);
 					}
 					try {
 						// Avoid user creating project in the persistent root folder.
-						engine.copyToFS("/home/web_user/projects/keep", new Uint8Array());
+						engine.copyToFS("/home/web_user/keep", new Uint8Array());
 					} catch(e) {
 						// File exists
 					}

platform/javascript/javascript_main.cpp

@@ -88,6 +88,13 @@ extern EMSCRIPTEN_KEEPALIVE int godot_js_main(int argc, char *argv[]) {
 
 	Main::start();
 	os->get_main_loop()->initialize();
+#ifdef TOOLS_ENABLED
+	if (Main::is_project_manager() && FileAccess::exists("/tmp/preload.zip")) {
+		PackedStringArray ps;
+		ps.push_back("/tmp/preload.zip");
+		os->get_main_loop()->emit_signal("files_dropped", ps, -1);
+	}
+#endif
 	emscripten_set_main_loop(main_loop_callback, -1, false);
 	// Immediately run the first iteration.
 	// We are inside an animation frame, we want to immediately draw on the newly setup canvas.