Add a ToolbarMenu component

[joebochill]

Describe the desired behavior

This will be a replacement for the existing DropdownToolbar component. We will build a generic component that will handle the dropdown arrow iconography and state and trigger the menu open and closed. The user will supply a ReactNode for the label (could be text, could be icon + text, etc.) and we will append the dropdown arrow beside their content. Clicking the content will open the menu described by the user (either through an items prop, or custom menu). Most of this functionality can simply be taken out of the existing dropdown toolbar.

Add deprecation warnings for the DropdownToolbar. Make sure that instructions for using the new approach is mentioned in the readme for the Appbar component (e.g., as an example).

Describe the current behavior

Rather than having this functionality built into a Toolbar, we will isolate it into a smaller sub-component that can be used in any toolbar (regular Mui Appbar, blui collapsible, etc.)

Is this request related to a current issue?

No

Additional Context

[ektasawant]

PR merge https://github.com/brightlayer-ui/react-component-library/pull/366. Closing this issue.