[FEAT] Deprecate DaffBackdropComponent and move logic inside of DaffSidebarComponent

[xelaint]

💡 Feature request

Feature Name

Deprecate DaffBackdropComponent and move logic inside of DaffSidebarComponent

The Desired Behavior

The backdrop component logic should be moved into the sidebar component. Backdrop doesn't need to be its own component as it probably will not be used anywhere else except the sidebar.

Your Use Case

As a developer, I'd like to clean up our design library.

Prior Work

Environment

Daffodil version: X.Y.Z
Angular version: X.Y.Z 

 
For Tooling issues:
- Node version: XX  
- Platform:  

Others:

[xelaint]

Dependent on #2569 to be completed first