Use case

Some applications would like to maintain extra padding when focusing items with directional or tab focus. Currently, Flutter aligns the top or bottom of the item with the top or bottom of the Scrollable it resides in. Adding additional padding allows applications that mainly depend on directional input to peek items in scrolling lists.

Proposal

• Add the ability to pass a padding to Scrollable.ensureVisible and ScrollPosition.ensureVisible (breaking change)
• Add a user-modifiable default padding to FocusManager (defaults to 0)
• Add a getter on FocusNode to get the padding for ensureVisible to support per-node paddings in the future