Allow determining whether sidebar is currently open or closed.

[Leila-Codes]

The original sidebar plugin (v1) provided an isVisible() function that would allow the user to determine whether the sidebar was open or closed.

This is particularly useful feature as it allows toggling of other element's (e.g. dialogs) styles and classes to better resize on the screen when the sidebar is open and closed.

Is it possible to provide something similar for this newer plugin?