add api to skip adding commands to undo queue

[abhinayagarwal]

Fixes #364

[jperedadnr]

This seems a good fix, but there are many internal uses of CommandManager::execute, which are only exposed via ActionCmdFactory (i.e. ActionCmdFactory::decorate calls ActionCmdDecorate::apply that calls viewModel.getCommandManager().execute(new DecorateCmd(Objects.requireNonNull(decorations)));).

So this API change would only work for direct usage of execute, which I don't think is happening, given that the CommandManager is typically used only internally by the RTA view model, and not by developers, isn't it?

[jperedadnr]

You don't need a new interface. ActionCmd could have:

public interface ActionCmd {
    void apply(RichTextAreaViewModel viewModel);

    default void apply(RichTextAreaViewModel viewModel, boolean skipUndo) {
        apply(viewModel);
    }
...

And then you could add the new apply where needed (ActionCmdXXX)

[jperedadnr]

DecorateAction and subclasses don't expose this.
BasicAction::execute doesn't expose this.

[abhinayagarwal]

DecorateAction doesn’t directly use the CommandManager. DecorateAction is extended by TextDecorateAction and ParagraphDecorateAction with both the later using ACTION_CMD_FACTORY.decorate internally. Should skipUndo be added as a constructor parameter to DecorateAction ?