Improve the editor native shader source visualizer

- Use CodeEdit to enable features such as line numbers and minimap.
- Enable syntax highlighting.
- Use a fixed-width font.
- Use the script editor settings.

editor/editor_native_shader_source_visualizer.h

@@ -33,11 +33,14 @@
 
 #include "scene/gui/dialogs.h"
 #include "scene/gui/tab_container.h"
+#include "scene/resources/syntax_highlighter.h"
 
 class EditorNativeShaderSourceVisualizer : public AcceptDialog {
 	GDCLASS(EditorNativeShaderSourceVisualizer, AcceptDialog)
 	TabContainer *versions = nullptr;
+	Ref<CodeHighlighter> syntax_highlighter;
 
+	void _load_theme_settings();
 	void _inspect_shader(RID p_shader);
 
 protected: