Tweak the name for new animations in the editor

- Use snake_case to "suggest" the naming that fits the Godot style guide.
- Fully spell out "new_animation" since both editors can fit it in full.
- Don't internationalize the new animation name to have consistent
  behavior between both editors.
  - Since the recommendation is to follow snake_case, special characters
    should also be avoided in the name to make animations easier to refer
    to in code.

editor/plugins/sprite_frames_editor_plugin.cpp

@@ -756,11 +756,11 @@ void SpriteFramesEditor::_animation_name_edited() {
 }
 
 void SpriteFramesEditor::_animation_add() {
-	String name = "New Anim";
+	String name = "new_animation";
 	int counter = 0;
 	while (frames->has_animation(name)) {
 		counter++;
-		name = "New Anim " + itos(counter);
+		name = vformat("new_animation_%d", counter);
 	}
 
 	List<Node *> nodes;