GDScript: Add autocompletion for `@export_tool_button`

modules/gdscript/gdscript_editor.cpp

@@ -48,7 +48,9 @@
 #ifdef TOOLS_ENABLED
 #include "core/config/project_settings.h"
 #include "editor/editor_file_system.h"
+#include "editor/editor_node.h"
 #include "editor/editor_settings.h"
+#include "editor/editor_string_names.h"
 #endif
 
 void GDScriptLanguage::get_comment_delimiters(List<String> *p_delimiters) const {
@@ -942,6 +944,19 @@ static void _find_annotation_arguments(const GDScriptParser::AnnotationNode *p_a
 			option.insert_text = option.display.quote(p_quote_style);
 			r_result.insert(option.display, option);
 		}
+	} else if (p_annotation->name == SNAME("@export_tool_button")) {
+		if (p_argument == 1) {
+			const Ref<Theme> theme = EditorNode::get_singleton()->get_editor_theme();
+			if (theme.is_valid()) {
+				List<StringName> icon_list;
+				theme->get_icon_list(EditorStringName(EditorIcons), &icon_list);
+				for (const StringName &E : icon_list) {
+					ScriptLanguage::CodeCompletionOption option(E, ScriptLanguage::CODE_COMPLETION_KIND_CLASS);
+					option.insert_text = option.display.quote(p_quote_style);
+					r_result.insert(option.display, option);
+				}
+			}
+		}
 	} else if (p_annotation->name == SNAME("@export_custom")) {
 		switch (p_argument) {
 			case 0: {