[Web] Add "threads"/"nothreads" feature tags to export presets

Following the "variant/thread_support" preset option.

platform/web/export/export_plugin.cpp

@@ -334,10 +334,14 @@ void EditorExportPlatformWeb::get_preset_features(const Ref<EditorExportPreset>
 	if (p_preset->get("vram_texture_compression/for_desktop")) {
 		r_features->push_back("s3tc");
 	}
-
 	if (p_preset->get("vram_texture_compression/for_mobile")) {
 		r_features->push_back("etc2");
 	}
+	if (p_preset->get("variant/thread_support").operator bool()) {
+		r_features->push_back("threads");
+	} else {
+		r_features->push_back("nothreads");
+	}
 	r_features->push_back("wasm32");
 }
 
@@ -345,7 +349,7 @@ void EditorExportPlatformWeb::get_export_options(List<ExportOption> *r_options)
 	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, "custom_template/debug", PROPERTY_HINT_GLOBAL_FILE, "*.zip"), ""));
 	r_options->push_back(ExportOption(PropertyInfo(Variant::STRING, "custom_template/release", PROPERTY_HINT_GLOBAL_FILE, "*.zip"), ""));
 
-	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "variant/extensions_support"), false)); // Export type.
+	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "variant/extensions_support"), false)); // GDExtension support.
 	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "variant/thread_support"), false)); // Thread support (i.e. run with or without COEP/COOP headers).
 	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "vram_texture_compression/for_desktop"), true)); // S3TC
 	r_options->push_back(ExportOption(PropertyInfo(Variant::BOOL, "vram_texture_compression/for_mobile"), false)); // ETC or ETC2, depending on renderer